Interplay between reference picture resampling and video coding tools

ABSTRACT

An example method of video processing includes determining, for a conversion between a current block of a current picture of a video and a bitstream of the video, whether to disable a coding tool for the current block; and performing the conversion based on the determining, wherein the coding tool is disabled when a dimension of a reference picture of one or more reference pictures of the current block is different from a dimension of the current picture, or a dimension of a scaling window in a reference picture of one or more reference pictures of the current block is different from a dimension of a scaling window in the current picture.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No. PCT/CN2020/120554, filed on Oct. 13, 2020, which claims the priority to and benefits of U.S. Provisional Patent Application No. 62/914,544, filed on Oct. 13, 2019. For all purposes under the law, the entire disclosure of the aforementioned application is incorporated by reference as part of the disclosure of this application.

TECHNICAL FIELD

This patent document relates to video coding techniques, devices and systems.

BACKGROUND

Currently, efforts are underway to improve the performance of current video codec technologies to provide better compression ratios or provide video coding and decoding schemes that allow for lower complexity or parallelized implementations. Industry experts have recently proposed several new video coding tools and tests are currently underway for determining their effectivity.

SUMMARY

Devices, systems and methods related to digital video coding, and specifically, to management of motion vectors are described. The described methods may be applied to existing video coding standards (e.g., High Efficiency Video Coding (HEVC) or Versatile Video Coding) and future video coding standards or video codecs.

In one representative aspect, the disclosed technology may be used to provide a method for video processing. This method includes performing a conversion between a current video block and a coded representation of the current video block, wherein, during the conversion, if a resolution and/or a size of a reference picture is different from a resolution and/or a size of the current video block, a same interpolation filter is applied to a group of adjacent or non-adjacent samples predicted using the current video block.

In another representative aspect, the disclosed technology may be used to provide another method for video processing. This method includes performing a conversion between a current video block and a coded representation of the current video block, wherein, during the conversion, if a resolution and/or a size of a reference picture is different from a resolution and/or a size of the current video block, wherein blocks predicted using the current video block are only allowed to use integer-valued motion information related to the current block.

In another representative aspect, the disclosed technology may be used to provide another method for video processing. This method includes performing a conversion between a current video block and a coded representation of the current video block, wherein, during the conversion, if a resolution and/or a size of a reference picture is different from a resolution and/or a size of the current video block, an interpolation filter is applied to derive blocks predicted using the current video block, and wherein the interpolation filter is selected based on a rule.

In another representative aspect, the disclosed technology may be used to provide another method for video processing. This method includes performing a conversion between a current video block and a coded representation of the current video block, wherein, during the conversion, if a resolution and/or a size of a reference picture is different from a resolution and/or a size of the current video block, selectively applying a deblocking filter, wherein a strength of the deblocking filter set in accordance with a rule related to the resolution and/or the size of the reference picture relative to the resolution and/or the size of the current video block.

In another representative aspect, the disclosed technology may be used to provide another method for video processing. This method includes performing a conversion between a current video block and a coded representation of the current video block, wherein, during the conversion, a reference picture of the current video block is resampled in accordance with a rule based on dimensions of the current video block.

In another representative aspect, the disclosed technology may be used to provide another method for video processing. This method includes performing a conversion between a current video block and a coded representation of the current video block, wherein, during the conversion, a use of a coding tool on the current video block is selectively enabled or disabled depending on a resolution/size of a reference picture of the current video block relative to a resolution/size of the current video block.

In another representative aspect, the disclosed technology may be used to provide another method for video processing. This method includes performing a conversion between multiple video blocks and coded representations of the multiple video blocks, wherein, during the conversion, a first conformance window is defined for a first video block and a second conformance window for a second video block, and wherein a ratio of a width and/or a height of the first conformance window to the second conformance window is in accordance with a rule based at least on a conformance bitstream.

In another representative aspect, the disclosed technology may be used to provide another method for video processing. This method includes performing a conversion between multiple video blocks and coded representations of the multiple video blocks, wherein, during the conversion, a first conformance window is defined for a first video block and a second conformance window for a second video block, and wherein a ratio of a width and/or a height of the first conformance window to the second conformance window is in accordance with a rule based at least on a conformance bitstream.

Further, in a representative aspect, an apparatus in a video system comprising a processor and a non-transitory memory with instructions thereon is disclosed. The instructions upon execution by the processor, cause the processor to implement any one or more of the disclosed methods.

In one representative aspect, a video decoding apparatus comprising a processor configured to implement a method recited herein is disclosed.

In one representative aspect, a video encoding apparatus comprising a processor configured to implement a method recited herein is disclosed.

Also, a computer program product stored on a non-transitory computer readable media, the computer program product including program code for carrying out any one or more of the disclosed methods is disclosed.

The above and other aspects and features of the disclosed technology are described in greater detail in the drawings, the description and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of sub-block motion vector (VSB) and motion vector difference.

FIG. 2 shows an example of a 16×16 video block divided into 16 4×4 regions.

FIG. 3A shows an example of a specific position in a sample.

FIG. 3B shows another example of a specific position in a sample.

FIG. 3C shows yet another example of a specific position in a sample.

FIG. 4A shows an example of positions of the current sample and its reference sample.

FIG. 4B shows another example of positions of the current sample and its reference sample.

FIG. 5 is a block diagram of an example of a hardware platform for implementing a visual media decoding or a visual media encoding technique described in the present document.

FIG. 6 shows a flowchart of an example method for video coding.

FIG. 7 shows an example of decoder side motion vector refinement.

FIG. 8 shows an example of flow of cascading DMVR and BDOF processes in VTM5.0. The DMVR SAD operations and BDOF SAD operations are different and not shared.

FIG. 9 is a block diagram of an example video processing system in which disclosed techniques may be implemented.

FIG. 10 is a block diagram that illustrates an example video coding system.

FIG. 11 is a block diagram that illustrates an encoder in accordance with some embodiments of the present disclosure.

FIG. 12 is a block diagram that illustrates a decoder in accordance with some embodiments of the present disclosure.

FIG. 13 is a flowchart representation of a method for video processing in accordance with the present technology.

FIG. 14 is a flowchart representation of another method for video processing in accordance with the present technology.

FIG. 15 is a flowchart representation of yet another method for video processing in accordance with the present technology.

DETAILED DESCRIPTION 1. Video Coding in HEVC/H.265

Video coding standards have evolved primarily through the development of the well-known ITU-T and ISO/IEC standards. The ITU-T produced H.261 and H.263, ISO/IEC produced MPEG-1 and MPEG-4 Visual, and the two organizations jointly produced the H.262/MPEG-2 Video and H.264/MPEG-4 Advanced Video Coding (AVC) and H.265/HEVC standards. Since H.262, the video coding standards are based on the hybrid video coding structure wherein temporal prediction plus transform coding are utilized. To explore the future video coding technologies beyond HEVC, Joint Video Exploration Team (JVET) was founded by VCEG and MPEG jointly in 2015. Since then, many new methods have been adopted by JVET and put into the reference software named Joint Exploration Model (JEM). In April 2018, the Joint Video Expert Team (JVET) between VCEG (Q6/16) and ISO/IEC JTC1 SC29/WG11 (MPEG) was created to work on the VVC standard targeting at 50% bitrate reduction compared to HEVC.

2. Overview

2.1. Adaptive Resolution Change (ARC)

AVC and HEVC does not have the ability to change resolution without having to introduce an IDR or intra random access point (IRAP) picture; such ability can be referred to as adaptive resolution change (ARC). There are use cases or application scenarios that would benefit from an ARC feature, including the following:

-   -   Rate adaption in video telephony and conferencing: For adapting         the coded video to the changing network conditions, when the         network condition gets worse so that available bandwidth becomes         lower, the encoder may adapt to it by encoding smaller         resolution pictures. Currently, changing picture resolution can         be done only after an IRAP picture; this has several issues. An         IRAP picture at reasonable quality will be much larger than an         inter-coded picture and will be correspondingly more complex to         decode: this costs time and resource. This is a problem if the         resolution change is requested by the decoder for loading         reasons. It can also break low-latency buffer conditions,         forcing an audio re-sync, and the end-to-end delay of the stream         will increase, at least temporarily. This can give a poor user         experience.     -   Active speaker changes in multi-party video conferencing: For         multi-party video conferencing, it is common that the active         speaker is shown in bigger video size than the video for the         rest of conference participants. When the active speaker         changes, picture resolution for each participant may also need         to be adjusted. The need to have ARC feature becomes more         important when such change in active speaker happens frequently.     -   Fast start in streaming: For streaming application, it is common         that the application would buffer up to certain length of         decoded picture before start displaying. Starting the bitstream         with smaller resolution would allow the application to have         enough pictures in the buffer to start displaying faster.

Adaptive stream switching in streaming: The Dynamic Adaptive Streaming over HTTP (DASH) specification includes a feature named @mediaStreamStructureId. This enables switching between different representations at open-GOP random access points with non-decodable leading pictures, e.g., CRA pictures with associated RASL pictures in HEVC. When two different representations of the same video have different bitrates but the same spatial resolution while they have the same value of @mediaStreamStructureId, switching between the two representations at a CRA picture with associated RASL pictures can be performed, and the RASL pictures associated with the switching-at CRA pictures can be decoded with acceptable quality hence enabling seamless switching. With ARC, the @mediaStreamStructureId feature would also be usable for switching between DASH representations with different spatial resolutions.

ARC is also known as Dynamic resolution conversion.

ARC may also be regarded as a special case of Reference Picture Resampling (RPR) such as H.263 Annex P.

2.2. Reference Picture Resampling in H.263 Annex P

This mode describes an algorithm to warp the reference picture prior to its use for prediction. It can be useful for resampling a reference picture having a different source format than the picture being predicted. It can also be used for global motion estimation, or estimation of rotating motion, by warping the shape, size, and location of the reference picture. The syntax includes warping parameters to be used as well as a resampling algorithm. The simplest level of operation for the reference picture resampling mode is an implicit factor of 4 resampling as only an FIR filter needs to be applied for the upsampling and downsampling processes. In this case, no additional signaling overhead is required as its use is understood when the size of a new picture (indicated in the picture header) is different from that of the previous picture.

2.3. Conformance Window in VVC

Conformance window in VVC defines a rectangle. Samples inside the conformance window belongs to the image of interest. Samples outside the conformance window may be discarded when output.

When conformance window is applied, the scaling ration in RPR is derived based on conformance windows.

Picture Parameter Set RBSP Syntax

pic_parameter_set_rbsp( ) { Descriptor  pps_pic_parameter set_id ue(v)  pps_seq_parameter_set_id ue(v)  pic_width_in luma samples ue(v)  pic_height_in_luma_samples ue(v)

 

 

 

 

 }

pic_width_in_luma_samples specifies the width of each decoded picture referring to the PPS in units of luma samples. pic_width_in_luma_samples shall not be equal to 0, shall be an integer multiple of Max(8, MinCbSizeY), and shall be less than or equal to pic_width_max_in_luma_samples.

When subpics_present_flag is equal to 1, the value of pic_width_in_luma_samples shall be equal to pic_width_max_in_luma_samples.

pic_height_in_luma_samples specifies the height of each decoded picture referring to the PPS in units of luma samples. pic_height_in_luma_samples shall not be equal to 0 and shall be an integer multiple of Max(8, MinCbSizeY), and shall be less than or equal to pic_height_max_in_luma_samples.

When subpics_present_flag is equal to 1, the value of pic_height_in_luma_samples shall be equal to pic_height_max_in_luma_samples.

Let refPicWidthInLumaSamples and refPicHeightInLumaSamples be the pic_width_in_luma_samples and pic_height_in_luma_samples, respectively, of a reference picture of a current picture referring to this PPS. Is a requirement of bitstream conformance that all of the following conditions are satisfied:

-   -   

    -   

    -   

    -   

conformance_window_flag equal to 1 indicates that the conformance cropping window offset parameters follow next in the SPS. conformance_window_flag equal to 0 indicates that the conformance cropping window offset parameters are not present.

conf_win_left_offset, conf_win_right_offset, conf_win_top_offset, and conf_win_bottom_offset specify the samples of the pictures in the CVS that are output from the decoding process, in terms of a rectangular region specified in picture coordinates for output. When conformance_window_flag is equal to 0, the values of conf_win_left_offset, conf_win_right_offset, conf_win_top_offset, and conf_win_bottom_offset are inferred to be equal to 0.

The conformance cropping window contains the luma samples with horizontal picture coordinates from SubWidthC*conf_win_left_offset to pic_width_in_luma_samples−(SubWidthC*conf_win_right_offset+1) and vertical picture coordinates from SubHeightC*conf_win_top_offset to pic_height_in_luma_samples−(SubHeightC*conf_win_bottom_offset+1), inclusive.

The value of SubWidthC*(conf_win_left_offset+conf_win_right_offset) shall be less than pic_width_in_luma_samples, and the value of SubHeightC*(conf_win_top_offset+conf_win_bottom_offset) shall be less than pic_height_in_luma_samples.

The variables PicOutputWidthL and PicOutputHeightL are derived as follows: PicOutputWidthL=pic_width_in_luma_samples−SubWidthC*(conf_win_right_offset+conf_win_left_offset)  (7-43) PicOutputHeightL=pic_height_in_pic_size_units−SubHeightC*(conf_win_bottom_offset+conf_win_top offset)  (7-44)

When ChromaArrayType is not equal to 0, the corresponding specified samples of the two chroma arrays are the samples having picture coordinates (x/SubWidthC, y/SubHeightC), where (x, y) are the picture coordinates of the specified luma samples.

Let ppsA and ppsB be any two PPSs referring to the same SPS. It is a requirement of bitstream conformance that, when ppsA and ppsB have the same the values of pic_width_in_luma_samples and pic_height_in_luma_samples, respectively, ppsA and ppsB shall have the same values of conf_win_left_offset, conf_win_right_offset, conf_win_top offset, and conf_win_bottom_offset, respectively.

2.4. Reference Picture Resampling (RPR)

In some embodiments, ARC is also known as Reference Picture Resampling (RPR). With RPR, TMVP is disabled if the collocated picture has a different resolution to the current picture. Besides, Bi-Directional Optical Flow (BDOF) and Decoder-side Motion Vector Refinement (DMVR) are disabled when the reference picture has a different resolution to the current picture.

To handle the normal MC when the reference picture has a different resolution than the current picture, the interpolation section is defined as below

8.5.6.3 Fractional Sample Interpolation Process

8.5.6.3.1 General

Inputs to this process are:

-   -   a luma location (xSb, ySb) specifying the top-left sample of the         current coding subblock relative to the top-left luma sample of         the current picture,     -   a variable sbWidth specifying the width of the current coding         subblock,     -   a variable sbHeight specifying the height of the current coding         subblock,     -   a motion vector offset mvOffset,     -   a refined motion vector refMvLX,     -   the selected reference picture sample array refPicLX,     -   the half sample interpolation filter index hpelIfIdx,     -   the bi-directional optical flow flag bdofFlag,     -   a variable cIdx specifying the colour component index of the         current block.

Outputs of this process are:

-   -   an (sbWidth+brdExtSize)×(sbHeight+brdExtSize) array         predSamplesLX of prediction sample values.

The prediction block border extension size brdExtSize is derived as follows: brdExtSize=(bdofFlag∥(inter_affine_flag[xSb][ySb]&& sps_affine_prof_enabled_flag))?2:0   (8-752)

The variable fRefWidth is set equal to the PicOutputWidthL of the reference picture in luma samples.

The variable fRefHeight is set equal to PicOutputHeightL of the reference picture in luma samples.

The motion vector mvLX is set equal to (refMvLX-mvOffset).

-   -   If cIdx is equal to 0, the following applies:         -   The scaling factors and their fixed-point representations             are defined as             hori_scale_fp=((fRefWidth<<14)+(PicOutputWidthL>>1))/PicOutputWidthL  (8-753)             vert_scale_fp=((fRefHeight<<14)+(PicOutputHeightL>>1))/PicOutputHeightL  (8-754)     -   Let (xIntL, yIntL) be a luma location given in full-sample units         and (xFracL, yFracL) be an offset given in 1/16-sample units.         These variables are used only in this clause for specifying         fractional-sample locations inside the reference sample arrays         refPicLX.         -   The top-left coordinate of the bounding block for reference             sample padding (xSbInt_(L), ySbInt_(L)) is set equal to             (xSb+(mvLX[0]>>4), ySb+(mvLX[1]>>4)).         -   For each luma sample location (x_(L)=0 . . .             sbWidth−1+brdExtSize, y_(L)=0 . . . sbHeight−1+brdExtSize)             inside the prediction luma sample array predSamplesLX, the             corresponding prediction luma sample value             predSamplesLX[x_(L)][y_(L)] is derived as follows:             -   Let (refxSb_(L), refySb_(L)) and (refx_(L), refy_(L)) be                 luma locations pointed to by a motion vector                 (refMvLX[0], refMvLX[1]) given in 1/16-sample units. The                 variables refxSb_(L), refx_(L), refySb_(L), and refy_(L)                 are derived as follows:                 refxSb_(L)=((xSb<<4)+refMvLX[0])*hori_scale_fp  (8-755)                 refx _(L)=((Sign(refxSb)*((Abs(refxSb)+128)>>8)+x                 _(L)*((hori_scale_fp+8)>>4))+32)>>6  (8-756)                 refySb_(L)=((ySb<<4)+refMvLX[1])*vert_scale_fp  (8-757)                 refyL=((Sign(refySb)*((Abs(refySb)+128)>>8)+y                 _(L)*((vert_scale_fp+8)>>4))+32)>>6  (8-758)     -   The variables xInt_(L), yInt_(L), xFrac_(L) and yFrac_(L) are         derived as follows:         xInt_(L)=refx _(L)>>4  (8-759)         yIntL=refy _(L)>>4  (8-760)         xFrac_(L)=refx _(L)&15  (8-761)         yFrac_(L)=refy _(L)&15  (8-762)     -   If bdofFlag is equal to TRUE or (sps_affine_prof_enabled_flag is         equal to TRUE and inter_affine_flag[xSb][ySb] is equal to TRUE),         and one or more of the following conditions are true, the         prediction luma sample value predSamplesLX[x_(L)][y_(L)] is         derived by invoking the luma integer sample fetching process as         specified in clause 8.5.6.3.3 with (xInt_(L)+(xFrac_(L)>>3)−1),         yInt_(L)+(yFrac_(L)>>3)−1) and refPicLX as inputs.         -   x_(L) is equal to 0.         -   x_(L) is equal to sbWidth+1.         -   y_(L) is equal to 0.         -   y_(L) is equal to sbHeight+1.     -   Otherwise, the prediction luma sample value         predSamplesLX[xL][yL] is derived by invoking the luma sample         8-tap interpolation filtering process as specified in clause         8.5.6.3.2 with (xIntL−(brdExtSize>0?1:0),         yIntL−(brdExtSize>0?1:0)), (xFracL, yFracL), (xSbInt_(L),         ySbInt_(L)), refPicLX, hpelIfIdx, sbWidth, sbHeight and (xSb,         ySb) as inputs.     -   Otherwise (cIdx is not equal to 0), the following applies:         -   Let (xIntC, yIntC) be a chroma location given in full-sample             units and (xFracC, yFracC) be an offset given in 1/32 sample             units. These variables are used only in this clause for             specifying general fractional-sample locations inside the             reference sample arrays refPicLX.         -   The top-left coordinate of the bounding block for reference             sample padding (xSbIntC, ySbIntC) is set equal to             ((xSb/SubWidthC)+(mvLX[0]>>5),             (ySb/SubHeightC)+(mvLX[1]>>5)).         -   For each chroma sample location (xC=0 . . . sbWidth−1, yC=0             . . . sbHeight−1) inside the prediction chroma sample arrays             predSamplesLX, the corresponding prediction chroma sample             value predSamplesLX[xC][yC] is derived as follows:             -   Let (refxSb_(C), refySb_(C)) and (refx_(C), refy_(C)) be                 chroma locations pointed to by a motion vector (mvLX[0],                 mvLX[1]) given in 1/32-sample units. The variables                 refxSb_(C), refySb_(C), refx_(C) and refy_(C) are                 derived as follows:                 refxSb_(C)=((xSb/SubWidthC<<5)+mvLX[0])*hori_scale_fp  (8-763)                 refx                 _(C)=((Sign(refxSb_(C))*((Abs(refxSb_(C))+256)>>9)+xC*((hori_scale_fp+8)>>4))+16)>>5  (8-764)                 refySb_(C)=((ySb/SubHeightC<<5)+mvLX[1])*vert_scale_fp  (8-765)                 refy                 _(C)=((Sign(refySb_(C))*((Abs(refySb_(C))+256)>>9)+yC*((vert_scale_fp+8)>>4))+16)>>5  (8-766)     -   The variables xInt_(C), yInt_(C), xFrac_(C) and yFrac_(C) are         derived as follows:         xInt_(C)=refx _(C)>>5  (8-767)         yInt_(C)=refy _(C)>>5  (8-768)         xFrac_(C)=refy _(C)& 31  (8-769)         yFrac_(C)=refy _(C)& 31  (8-770)     -   The prediction sample value predSamplesLX[xC][yC] is derived by         invoking the process specified in clause 8.5.6.3.4 with (xIntC,         yIntC), (xFracC, yFracC), (xSbIntC, ySbIntC), sbWidth, sbHeight         and refPicLX as inputs.         8.5.6.3.2 Luma sample interpolation filtering process

Inputs to this process are:

-   -   a luma location in full-sample units (xInt_(L), yInt_(L)),     -   a luma location in fractional-sample units (xFrac_(L),         yFrac_(L)),     -   a luma location in full-sample units (xSbInt_(L), ySbInt_(L))         specifying the top-left sample of the bounding block for         reference sample padding relative to the top-left luma sample of         the reference picture,     -   the luma reference sample array refPicLX_(L),     -   the half sample interpolation filter index hpelIfIdx,     -   a variable sbWidth specifying the width of the current subblock,     -   a variable sbHeight specifying the height of the current         subblock,     -   a luma location (xSb, ySb) specifying the top-left sample of the         current subblock relative to the top-left luma sample of the         current picture,

Output of this process is a predicted luma sample value predSampleLX_(L)

The variables shift1, shift2 and shift3 are derived as follows:

-   -   The variable shift1 is set equal to Min(4, BitDepth_(Y)−8), the         variable shift2 is set equal to 6 and the variable shift3 is set         equal to Max(2, 14−BitDepth_(Y)).     -   The variable picW is set equal to pic_width_in_luma_samples and         the variable picH is set equal to pic_height_in_luma_samples.

The luma interpolation filter coefficients f_(L)[p] for each 1/16 fractional sample position p equal to xFrac_(L) or yFrac_(L) are derived as follows:

-   -   If MotionModelIdc[xSb][ySb] is greater than 0, and sbWidth and         sbHeight are both equal to 4, the luma interpolation filter         coefficients f_(L)[p] are specified in Table 2.     -   Otherwise, the luma interpolation filter coefficients f_(L)[p]         are specified in Table 1 depending on hpelIfIdx.

The luma locations in full-sample units (xInt_(i), yInt_(i)) are derived as follows for i=0 . . . 7:

-   -   If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the         following applies:         xInt_(i)=Clip3(SubPicLeftBoundaryPos,SubPicRightBoundaryPos,xInt_(L)         +i−3)  (8-771)         yInt_(i)=Clip3(SubPicTopBoundaryPos,SubPicBotBoundaryPos,yInt_(L)         +i−3)  (8-772)     -   Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to 0),         the following applies:         xInt_(i)=Clip3(0,picW−1,sps_ref_wraparound_enabled_flag?ClipH((sps_ref_wraparound_offset_minus1+1)*MinCbSizeY,picW,xInt_(L)         +i−3):xInt_(L) +i−3)  (8-773)         yInt_(i)=Clip3(0,picH−1,yInt_(L) +i−3)  (8-774)

The luma locations in full-sample units are further modified as follows for i=0 . . . 7: xInt_(i)=Clip3(xSbInt_(L)−3,xSbInt_(L)+sbWidth+4,xInt_(i))  (8-775) yInt_(i)=Clip3(ySbInt_(L)−3,ySbInt_(L)+sbHeight+4,yInt_(i))  (8-776)

The predicted luma sample value predSampleLX_(L) is derived as follows:

-   -   If both xFrac_(L) and yFrac_(L) are equal to 0, the value of         predSampleLX_(L) is derived as follows:         predSampleLX_(L)=refPicLX_(L)[xInt₃][yInt₃]<<shift3  (8-777)     -   Otherwise, if xFrac_(L) is not equal to 0 and yFrac_(L) is equal         to 0, the value of predSampleLX_(L) is derived as follows:         predSampleLX_(L)=(Σ_(i=0) ⁷ f         _(L)[xFrac_(L)][i]*refPicLX_(L)[xInt_(i)][yInt₃])>>shift1  (8-778)     -   Otherwise, if xFrac_(L) is equal to 0 and yFrac_(L) is not equal         to 0, the value of predSampleLX_(L) is derived as follows:         predSampleLX_(L)=(Σ_(i=0) ⁷ f         _(L)[yFrac_(L)][i]*refPicLX_(L)[xInt₃][yInt_(i)])>>shift1  (8-779)     -   Otherwise, if xFraC_(L) is not equal to 0 and yFrac_(L) is not         equal to 0, the value of predSampleLX_(L) is derived as follows:         -   The sample array temp[n] with n=0 . . . 7, is derived as             follows:             temp[n]=(Σ_(i=0) ⁷ f             _(L)[xFrac_(L)][i]*refPicLX_(L)[xInt_(i)][yInt_(a)])>>shift1  (8-780)     -   The predicted luma sample value predSampleLX_(L) is derived as         follows:         predSampleLX_(L)=(Σ_(i=0) ⁷ f         _(L)[yFrac_(L)][i]*temp[i])>>shift2  (8-781)

TABLE 8-11 Specification of the luma interpolation filter coefficients f_(L)[p] for each 1/16 fractional sample position p. Fractional sample interpolation filter coefficients position p f_(L)[p][0] f_(L)[p][1] f_(L)[p][2] f_(L)[p][3] f_(L)[p][4] f_(L)[p][5] f_(L)[p][6] f_(L)[p][7] 1 0 1 −3 63 4 −2 1 0 2 −1 2 −5 62 8 −3 1 0 3 −1 3 −8 60 13 −4 1 0 4 −1 4 −10 58 17 −5 1 0 5 −1 4 −11 52 26 −8 3 −1 6 −1 3 −9 47 31 −10 4 −1 7 −1 4 −11 45 34 −10 4 −1 8 (hpelIfIdx == 0) −1 4 −11 40 40 −11 4 −1 8 (hpelIfIdx == 1) 0 3 9 20 20 9 3 0 9 −1 4 −10 34 45 −11 4 −1 10 −1 4 −10 31 47 −9 3 −1 11 −1 3 −8 26 52 −11 4 −1 12 0 1 −5 17 58 −10 4 −1 13 0 1 −4 13 60 −8 3 −1 14 0 1 −3 8 62 −5 2 −1 15 0 1 −2 4 63 −3 1 0

TABLE 8-12 Specification of the luma interpolation filter coefficients f_(L)[p] for each 1/16 fractional sample position p for affine motion mode. Fractional sample interpolation filter coefficients position p f_(L)[p][0] f_(L)[p][1] f_(L)[p][2] f_(L)[p][3] f_(L)[p][4] f_(L)[p][5] f_(L)[p][6] f_(L)[p][7] 1 0 1 −3 63 4 −2 1 0 2 0 1 −5 62 8 −3 1 0 3 0 2 −8 60 13 −4 1 0 4 0 3 −10 58 17 −5 1 0 5 0 3 −11 52 26 −8 2 0 6 0 2 −9 47 31 −10 3 0 7 0 3 −11 45 34 −10 3 0 8 0 3 −11 40 40 −11 3 0 9 0 3 −10 34 45 −11 3 0 10 0 3 −10 31 47 −9 2 0 11 0 2 −8 26 52 −11 3 0 12 0 1 −5 17 58 −10 3 0 13 0 1 −4 13 60 −8 2 0 14 0 1 −3 8 62 −5 1 0 15 0 1 −2 4 63 −3 1 0 8.5.6.3.3 Luma Integer Sample Fetching Process

Inputs to this process are:

-   -   a luma location in full-sample units (xInt_(L), yInt_(L))     -   the luma reference sample array refPicLX_(L),

Output of this process is a predicted luma sample value predSampleLX_(L)

The variable shift is set equal to Max(2, 14−BitDepth_(Y)).

The variable picW is set equal to pic_width_in_luma_samples and the variable picH is set equal to pic_height_in_luma_samples.

The luma locations in full-sample units (xInt, yInt) are derived as follows: xInt=Clip3(0,picW−1,sps_ref_wraparound_enabled_flag?ClipH((sps_ref_wraparound_offset_minus1+1)*MinCbSizeY,picW,xInt_(L)):xInt_(L))  (8-782) yInt=Clip3(0,picH−1,yInt_(L))  (8-783)

The predicted luma sample value predSampleLX_(L) is derived as follows: predSampleLX_(L)=refPicLX_(L)[xInt][yInt]<<shift3   (8-784) 8.5.6.3.4 Chroma Sample Interpolation Process

Inputs to this process are:

-   -   a chroma location in full-sample units (xInt_(C), yInt_(C)),     -   a chroma location in 1/32 fractional-sample units (xFrac_(C),         yFrac_(C)),     -   a chroma location in full-sample units (xSbIntC, ySbIntC)         specifying the top-left sample of the bounding block for         reference sample padding relative to the top-left chroma sample         of the reference picture,     -   a variable sbWidth specifying the width of the current subblock,     -   a variable sbHeight specifying the height of the current         subblock,     -   the chroma reference sample array refPicLX_(C).

Output of this process is a predicted chroma sample value predSampleLX_(C)

The variables shift1, shift2 and shift3 are derived as follows:

-   -   The variable shift1 is set equal to Min(4, BitDepth_(C)−8), the         variable shift2 is set equal to 6 and the variable shift3 is set         equal to Max(2, 14−BitDepth_(C)).     -   The variable picW_(C) is set equal to         pic_width_in_luma_samples/SubWidthC and the variable picH_(C) is         set equal to pic_height_in_luma_samples/SubHeightC.

The chroma interpolation filter coefficients f_(C)[p] for each 1/32 fractional sample position p equal to xFrac_(C) or yFrac_(C) are specified in Table 3.

The variable xOffset is set equal to (sps_ref_wraparound_offset_minus1+1)*MinCbSizeY)/SubWidthC.

The chroma locations in full-sample units (xInt_(i), yInt_(i)) are derived as follows for i=0 . . . 3:

-   -   If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the         following applies:         xInt_(i)=Clip3(SubPicLeftBoundaryPos/SubWidthC,SubPicRightBoundaryPos/SubWidthC,xInt_(L)         +i)   (8-785)         yInt_(i)=Clip3(SubPicTopBoundaryPos/SubHeightC,SubPicBotBoundaryPos/SubHeightC,yInt_(L)         +i)   (8-786)     -   Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to 0),         the following applies:         xInt_(i)=Clip3(0,picW         _(C)−1,sps_ref_wraparound_enabled_flag?ClipH(xOffset,picW _(C)         ,xInt_(C) +i−1):xInt_(C) +i−1)  (8-787)         xInt _(C) +i−1)yInt_(i)=Clip3(0,picH _(C)−1,yInt_(C)         +i−1)  (8-788)

The chroma locations in full-sample units (xInt_(i), yInt_(i)) are further modified as follows for i=0 . . . 3: xInt_(i)=Clip3(xSbIntC−1,xSbIntC+sbWidth+2,xInt_(i))  (8-789) yInt_(i)=Clip3(ySbIntC−1,ySbIntC+sbHeight+2,yInt_(i))  (8-790)

The predicted chroma sample value predSampleLX_(C) is derived as follows:

-   -   If both xFrac_(C) and yFrac_(C) are equal to 0, the value of         predSampleLX_(C) is derived as follows:         predSampleLX_(C)=refPicLX_(C)[xInt_(i)][yInt_(i)]<<shift3  (8-791)     -   Otherwise, if xFrac_(C) is not equal to 0 and yFrac_(C) is equal         to 0, the value of predSampleLX_(C) is derived as follows:         predSampleLX_(C)=(Σ_(i=0) ³ f         _(C)[xFrac_(C)][i]*refPicLX_(C)[xInt_(i)][yInt₁])>>shift1  (8-792)     -   Otherwise, if xFrac_(C) is equal to 0 and yFrac_(C) is not equal         to 0, the value of predSampleLX_(C) is derived as follows:         predSampleLX_(C)=(Σ_(i=0) ³ f         _(C)[yFrac_(C)][i]*refPicLX_(C)[xInt₁][yInt_(i)])>>shift1  (8-793)     -   Otherwise, if xFrac_(C) is not equal to 0 and yFrac_(C) is not         equal to 0, the value of predSampleLX_(C) is derived as follows:         -   The sample array temp[n] with n=0 . . . 3, is derived as             follows:             temp[n]=(Σ_(i=0) ³ f             _(C)[xFrac_(C)][i]*refPicLX_(C)[xInt_(i)][yInt_(n)])>>shift1  (8-794)     -   The predicted chroma sample value predSampleLX_(C) is derived as         follows:         predSampleLX_(C)=(f _(C)[yFrac_(C)][0]*temp[0]+f         _(C)[yFrac_(C)][1]*temp[1]+f _(C)[yFrac_(C)][2]*temp[2]+f         _(C)[yFrac_(C)][3]*temp[3])>>shift2  (8-795)

TABLE 8-13 Specification of the chroma interpolation filter coefficients f_(c)[p] for each 1/32 fractional sample position p. Fractional sample interpolation filter coefficients position p f_(c)[p][0] f_(c)[p][1] f_(c)[p][2] f_(c)[p][3] 1 −1 63 2 0 2 −2 62 4 0 3 −2 60 7 −1 4 −2 58 10 −2 5 −3 57 12 −2 6 −4 56 14 −2 7 −4 55 15 −2 8 −4 54 16 −2 9 −5 53 18 −2 10 −6 52 20 −2 11 −6 49 24 −3 12 −6 46 28 −4 13 −5 44 29 −4 14 −4 42 30 −4 15 −4 39 33 −4 16 −4 36 36 −4 17 −4 33 39 −4 18 −4 30 42 −4 19 −4 29 44 −5 20 −4 28 46 −6 21 −3 24 49 −6 22 −2 20 52 −6 23 −2 18 53 −5 24 −2 16 54 −4 25 −2 15 55 −4 26 −2 14 56 −4 27 −2 12 57 −3 28 −2 10 58 −2 29 −1 7 60 −2 30 0 4 62 −2 31 0 2 63 −1 2.5. Refined Sub-Block Based Affine Motion Compensated Prediction

The techniques disclosed herein include a method to refine the sub-block based affine motion compensated prediction with optical flow. After the sub-block based affine motion compensation is performed, prediction sample is refined by adding a difference derived by the optical flow equation, which is referred as prediction refinement with optical flow (PROF). The proposed method can achieve inter prediction in pixel level granularity without increasing the memory access bandwidth.

To achieve a finer granularity of motion compensation, this contribution proposes a method to refine the sub-block based affine motion compensated prediction with optical flow. After the sub-block based affine motion compensation is performed, luma prediction sample is refined by adding a difference derived by the optical flow equation. The proposed PROF (prediction refinement with optical flow) is described as following four steps.

Step 1) The sub-block-based affine motion compensation is performed to generate sub-block prediction I(i, j).

Step 2) The spatial gradients g_(x)(i, j) and g_(y)(i, j) of the sub-block prediction are calculated at each sample location using a 3-tap filter [−1, 0, 1]. g _(x)(i,j)=I(i+1,j)−I(i−1,j) g _(y)(i,j)=I(i,j+1)−I(i,j−1)

The sub-block prediction is extended by one pixel on each side for the gradient calculation. To reduce the memory bandwidth and complexity, the pixels on the extended borders are copied from the nearest integer pixel position in the reference picture. Therefore, additional interpolation for padding region is avoided.

Step 3) The luma prediction refinement (denoted ΔI) as is calculated by the optical flow equation. ΔI(i,j)=g _(x)(i,j)*Δv _(x)(i,j)+g _(y)(i,j)*Δv _(y)(i,j) where the delta MV (denoted as Δv(i, j)) is the difference between pixel MV computed for sample location (i, j), denoted by v(i, j), and the sub-block MV of the sub-block to which pixel (i, j) belongs, as shown in FIG. 1 .

Since the affine model parameters and the pixel location relative to the sub-block center are not changed from sub-block to sub-block, Δv(i, j) can be calculated for the first sub-block, and reused for other sub-blocks in the same CU. Let x and y be the horizontal and vertical offset from the pixel location to the center of the sub-block, Δv(x, y) can be derived by the following equation,

$\quad\left\{ \begin{matrix} {{\Delta\;{v_{x}\left( {x,y} \right)}} = {{c*x} + {d*y}}} \\ {{\Delta\;{v_{y}\left( {x,y} \right)}} = {{e*x} + {f*y}}} \end{matrix} \right.$

For 4-parameter affine model,

$\quad\left\{ \begin{matrix} {c = {f = \frac{v_{1x} - v_{0x}}{w}}} \\ {e = {{- d} = \frac{v_{1y} - v_{0y}}{w}}} \end{matrix} \right.$

For 6-parameter affine model,

$\quad\left\{ \begin{matrix} {c = \frac{v_{1x} - v_{0x}}{w}} \\ {d = \frac{v_{2x} - v_{0x}}{h}} \\ {e = \frac{v_{1y} - v_{0\; y}}{w}} \\ {f = \frac{v_{2y} - v_{0y}}{h}} \end{matrix} \right.$ where (v_(0x), v_(0y)), (v_(1x), v_(1y)), (v_(2x), v_(2y)) are the top-left, top-right and bottom-left control point motion vectors, w and h are the width and height of the CU. Step 4) Finally, the luma prediction refinement is added to the sub-block prediction I(i, j). The final prediction I′ is generated as the following equation. I′(i,j)=I(i,j)+ΔI(i,j)

Some details are described below:

a) How to Derive the Gradients for PROF

In some embodiments, the gradients are calculated for each sub-block (4×4 sub-block in VTM-4.0) for each reference list. For each sub-block, the nearest integer samples of the reference block are fetched to pad the four side outer lines of samples.

Suppose the MV for the current sub-block is (MVx, MVy). Then the fractional part is calculated as (FracX, FracY)=(MVx&15, MVy&15). The integer part is calculated as (IntX, IntY)=(MVx>>4, MVy>>4). The offsets (OffsetX, OffsetY) are derived as: OffsetX=FracX>7?1:0; OffsetY=FracY>7?1:0;

Suppose the top-left coordinate of the current sub-block is (xCur, yCur) and the dimensions of the current sub-block is W×H. Then (xCor0, yCor0), (xCor1, yCor1), (xCor2, yCor2) and (xCor3, yCor3) are calculated as: (xCor0,yCor0)=(xCur+IntX+OffsetX−1,yCur+IntY+OffsetY−1); (xCor1,yCor1)=(xCur+IntX+OffsetX−1,yCur+IntY+OffsetY+H); (xCor2,yCor2)=(xCur+IntX+OffsetX−1,yCur+IntY+OffsetY); (xCor3,yCor3)=(xCur+IntX+OffsetX+W,yCur+IntY+OffsetY);

Suppose PredSample[x][y] with x=0 . . . W−1, y=0 . . . H−1 stores the prediction samples for the sub-block. Then the padding samples are derived as: PredSample[x][−1]=(Ref(xCor0+x,yCor0)<<Shift0)−Rounding, for x=−1 . . . W; PredSample[x][H]=(Ref(xCor1+x,yCor1)<<Shift0)−Rounding, for x=−1 . . . W; PredSample[−1][y]=(Ref(xCor2,yCor2+y)<<Shift0)−Rounding, for y=0 . . . H−1; PredSample[W][y]=(Ref(xCor3,yCor3+y)<<Shift0)−Rounding, for y=0 . . . H−1;

where Rec represents the reference picture. Rounding is an integer, which is equal to 2¹³ in the exemplary PROF implementation. Shift0=Max(2, (14−BitDepth)); PROF attempts to increase the precision of the gradients, unlike BIO in VTM-4.0, where the gradients are output with the same precision as input luma samples.

The gradients in PROF are calculated as below: Shift1=Shift0−4. gradientH[x][y]=(predSamples[x+1][y]−predSample[x−1][y])>>Shift1 gradientV[x][y]=(predSample[x][y+1]−predSample[x][y−1])>>Shift1

It should be noted that predSamples[x][y] keeps the precision after interpolation.

b) How to Derive Δv for PROF

The derivation of Δv (denoted as dMvH[posX][posY] and dMvV[posX][posY] with posX=0 . . . W−1, posY=0 . . . H−1) can be described as below.

Suppose the dimensions of the current block is cbWidth×cbHeight, the number of control point motion vectors is numCpMv, and the control point motion vectors are cpMvLX[cpIdx], with cpIdx=0 . . . numCpMv−1 and X being 0 or 1 representing the two reference lists.

The variables log 2CbW and log 2CbH are derived as follows: log 2CbW=Log 2(cbWidth) log 2CbH=Log 2(cbHeight)

The variables mvScaleHor, mvScaleVer, dHorX and dVerX are derived as follows: mvScaleHor=cpMvLX[0][0]<<7 mvScaleVer=cpMvLX[0][1]<<7 dHorX=(cpMvLX[1][0]−cpMvLX[0][0])<<(7−log 2CbW) dVerX=(cpMvLX[1][1]−cpMvLX[0][1])<<(7−log 2CbW)

The variables dHorY and dVerY are derived as follows:

-   -   If numCpMv is equal to 3, the following applies:         dHorY=(cpMvLX[2][0]−cpMvLX[0][0])<<(7−log 2CbH)         dVerY=(cpMvLX[2][1]−cpMvLX[0][1])<<(7−log 2CbH)     -   Otherwise (numCpMv is equal to 2), the following applies:         dHorY=−dVerX         dVerY=dHorX

The variable qHorX, qVerX, qHorY and qVerY are derived as: qHorX=dHorX<<2; qVerX=dVerX<<2; qHorY=dHorY<<2; qVerY=dVerY<<2;

dMvH[0][0] and dMvV[0][0] are calculated as: dMvH[0][0]=((dHorX+dHorY)<<1)−((qHorX+qHorY)<<1); dMvV[0][0]=((dVerX+dVerY)<<1)−((qVerX+qVerY)<<1);

dMvH[xPos][0] and dMvV[xPos][0] for xPos from 1 to W−1 are derived as: dMvH[xPos][0]=dMvH[xPos−1][0]+qHorX; dMvV[xPos][0]=dMvV[xPos−1][0]+qVerX;

For yPos from 1 to H−1, the following applies: dMvH[xPos][yPos]=dMvH[xPos][yPos−1]+qHorY with xPos=0 . . . W−1 dMvV[xPos][yPos]=dMvV[xPos][yPos−1]+qVerY with xPos=0 . . . W−1

Finally, dMvH[xPos][yPos] and dMvV[xPos][yPos] with posX=0 . . . W−1, posY=0 . . . H−1 are right shifted as: dMvH[xPos][yPos]=SatShift(dMvH[xPos][yPos],7+2−1); dMvV[xPos][yPos]=SatShift(dMvV[xPos][yPos],7+2−1);

where SatShift(x, n) and Shift (x,n) is defined as:

${{SatShift}\left( {x,n} \right)} = \left\{ \begin{matrix} {\left( {x + {{offset}\; 0}} \right) ⪢ n} & {{{if}\mspace{14mu} x} \geq 0} \\ {- \left( {\left( {{- x} + {{offset}\; 1}} \right) ⪢ n} \right)} & {{{if}\mspace{14mu} x} < 0} \end{matrix} \right.$ Shift(x,n)=(x+offset0)>>n

In one example, offset0 and/or offset1 are set to (1<<n)>>1.

c) How to Derive ΔI for PROF

For a position (posX, posY) inside a sub-block, its corresponding Δv(i, j) is denoted as (dMvH[posX][posY], dMvV[posX][posY]). Its corresponding gradients are denoted as (gradientH[posX][posY], gradientV[posX][posY]).

Then ΔI(posX, posY) is derived as follows.

(dMvH[posX][posY], dMvV[posX][posY]) are clipped as: dMvH[posX][posY]=Clip3(−32768,32767,dMvH[posX][posY]); dMvV[posX][posY]=Clip3(−32768,32767,dMvV[posX][posY]); ΔI(posX,posY)=dMvH[posX][posY]×gradientH[posX][posY]+dMvV[posX][posY]×gradientV[posX][posY]; ΔI(posX,posY)=Shift(ΔI(posX,posY),1+1+4); ΔI(posX,posY)=Clip3(−(2¹³−1),2¹³−1,ΔI(posX,posY));

d) How to Derive I′ for PROF

If the current block is not coded as bi-prediction or weighted-prediction, I′(posX,posY)=Shift((I(posX,posY)+ΔI(posX,posY)),Shift0), I′(posX,posY)=ClipSample(I′(posX,posY)),

where ClipSample clips a sample value to a valid output sample value. Then I′(posX, posY) is output as the inter-prediction value.

Otherwise (the current block is coded as bi-prediction or weighted-prediction). I′(posX, posY) will be stored and used to generate the inter-prediction value according to other prediction values and/or weighting values.

2.6. Example Slice Header

slice_header( ) { Descriptor  slice_pic_parameter_set_id ue(v)  if( rect_slice_flag ∥ NumBricksInPic > 1 )   slice_address u(v)  if( !rect_slice_flag && !single_brick_per_slice_flag)   num_bricks_in_slice_minus1 ue(v)  non_reference_picture_flag u(1)  slice_type ue(v)  if( separate_colour_plane_flag == 1 )   colour_plane_id u(2)  slice_pic_order_cnt_lsb u(v)  if( nal_unit_type == GDR_NUT)   recovery_poc_cnt ue(v)  if( nal_unit_type == IDR_W_RADL ∥ nal_unit_type == IDR_N_LP ∥  nal_unit_type == CRA_NUT ∥ NalUnitType == GDR_NUT)   no_output_of_prior_pics_flag u(1)  if( output_flag_present_flag)   pic_output_flag u(1)  if( ( nal_unit_type != IDR_W_RADL && nal_unit_type != IDR_N_LP ) ∥   sps_idr_rpl_present_flag) {   for(i = 0; i < 2; i++ ) {   if( num_ref_pic_lists_in_sps[ i ] > 0 && !pps_ref_pic_list_sps_idc[ i ] &&      ( i == 0 ∥ ( i = = 1 && rpl1_idx_present_flag)))    ref_pic_list_sps_flag[ i ] u(1)   if( ref_pic_list_sps_flag[ i ] ) {    if( num_ref_pic_lists_in_sps[ i ] > 1 &&      ( i = = 0 ∥ ( i = = 1 && rpl1_idx_present_flag)))     ref_pic_list_idx[ i ] u(v)   } else    ref_pic_list_struct(i, num_ref_pic_lists_in_sps[ i ] )   for(j = 0; j < NumLtrpEntries[ i ][ RplsIdx[ i ] ]; j++ ) {    if( ltrp_in_slice_header_flag[ i ][ RplsIdx][ i ] ] )    slice_poc_lsb_lt[ i ][ j ] u(v)    delta_poc_msb_present_flag[ i ][ j ] u(1)    if( delta_poc_msb_present_flag[ i ][ j ] )    delta_poc_msb_cycle_lt[ i ][ j ] ue(v)   }  }  if( ( slice_type != I && num_ref_entries[ 0 ][RplsIdx [ 0 ] ] > 1 ) ∥   ( slice_type == B && num_ref_entries[ 1 ][ RplsIdx[ 1 ] ] > 1 ) ) {   num_ref_idx_active_override_flag u(1)   if( num_ref_idx_active_override_flag)    for( i = 0; i < ( slice_type == B ? 2: 1 ); i++ )    if( num_ref_entries[ i ][ RplsIdx[ i ] ] > 1 )     num_ref_idx_active_minus1[ i ] ue(v)   }  }  if( partition_constraints_override_enabled_flag) {   partition_constraints_override_flag ue(v)   if( partition_constraints_override_flag) {   slice_log2_diff_min_qt_min_cb_luma ue(v)   slice_max_mtt_hierarchy_depth_luma ue(v)   if( slice_max_mtt_hierarchy_depth_luma!=0 )    slice_log2_diff_max_bt_min_qt_luma ue(v)    slice_log2_diff_max_tt_min_qt_luma ue(v)   }   if( slice_type == I && qtbtt_dual_tree_intra_flag) {    slice_log2_diff_min_qt_min_cb_chroma ue(v)    slice_max_mtt_hierarchy_depth_chroma ue(v)    if( slice_max_mtt_hierarchy_depth_chroma != 0 )    slice_log2_diff_max_bt_min_qt_chroma ue(v)    slice_log2_diff_max_tt_min_qt_chroma ue(v)    }   }   }  }  if ( slice_type != I ) {   if( sps_temporal_mvp_enabled_flag && !pps_temporal_mvp_enabled_idc)   slice_temporal_mvp_enabled_flag u(1)   if( slice_type == B && !pps_mvd_l1_zero_idc)   mvd_l1_zero_flag u(1)   if( cabac_init_present_flag)   cabac_init_flag u(1)   if( slice_temporal_mvp_enabled_flag) {   if( slice_type == B && !pps_collocated_from_l0_idc )    collocated_from_l0_flag u(1)   if( ( collocated_from_l0_flag && NumRefIdxActive[ 0 ] > 1 ) ∥    ( !collocated_from_l0_flag && NumRefIdxActive[ 1 ] > 1 ) )    collocated_ref_idx ue(v)   }   if( ( pps_weighted_pred_flag && slice_type == P ) ∥   ( pps_weighted_bipred_flag && slice_type == B ) )   pred_weight_table( )   if( !pps_six_minus_max_num_merge_cand_plus1)   six_minus_max_num_merge_cand ue(v)   if( sps_affine_enabled_flag &&    !pps_five_minus_max_num_subblock_merge_cand_plus1)   five_minus_max_num_subblock_merge_cand ue(v)   if( sps_fpel_mmvd_enabled_flag)   slice_fpel_mmvd_enabled_flag u(1)   if( sps_bdof_dmvr_slice_present_flag)   slice_disable_bdof_dmvr_flag u(1)   if( sps_triangle_enabled_flag && MaxNumMergeCand >= 2 &&    !pps_max_num_merge_cand_minus_max_num_triangle_cand_minus1)   max_num_merge_cand_minus_max_num_triangle_cand ue(v)  }  if ( sps_ibc_enabled_flag)   slice_six_minus_max_num_ibc_merge_cand ue(v)  if( sps_joint_cbcr_enabled_flag )   slice_joint_cbcr_sign_flag u(1)  slice_qp_delta se (v)  if( pps_slice_chroma_qp_offsets_present_flag) {   slice_cb_qp_offset se (v)   slice_cr_qp_offset se (v)   if( sps_joint_cbcr_enabled_flag)   slice_joint_cbcr_qp_offset se (v)  }  if( sps_sao_enabled_flag) {   slice_sao_luma_flag u(1)   if( ChromaArrayType != 0 )   slice_sao_chroma_flag u(1)  }  if( sps_alf_enabled_flag) {   slice_alf_enabled_flag u(1)   if( slice_alf_enabled_flag) {   slice_num_alf_aps_ids_luma u(3)   for( i = 0; i < slice_num_alf_aps_ids_luma; i++ )    slice_alf_aps_id_luma[ i ] u(3)   if( ChromaArrayType != 0 )    slice_alf_chroma_idc u(2)   if( slice_alf_chroma_idc )    slice_alf_aps_id_chroma u(3)   }  }  if ( !pps_dep_quant_enabled_flag)   dep_quant_enabled_flag u(1)  if( !dep_quant_enabled_flag)   sign_data_hiding_enabled_flag u(1)  if( deblocking_filter_override_enabled_flag)   deblocking_filter_override_flag u(1)  if( deblocking_filter_override_flag) {   slice_deblocking_filter_disabled_flag u(1)   if( !slice_deblocking_filter_disabled_flag) {   slice_beta_offset_div2 se(v)   slice_tc_offset_div2 se(v)   }  }  if( sps_lmcs_enabled_flag) {   slice_lmcs_enabled_flag u(1)   if( slice_lmcs_enabled_flag) {   slice_lmcs_aps_id u(2)   if( ChromaArrayType != 0 )    slice_chroma_residual_scale_flag u(1)   }  }  if( sps_scaling_list_enabled_flag) {   slice_scaling_list_present_flag u(1)   if( slice_scaling_list_present_flag)   slice_scaling_list_aps_id u(3)  }  if( entry_point_offsets_present_flag &&  NumEntryPoints > 0 ) {   offset_len_minus1 ue(v)   for( i = 0; i < NumEntryPoints; i++ )   entry_point_offset_minus1[ i ] u(v)  }  if( slice_header_extension_present_flag) {   slice_header_extension_length ue(v)   for( i = 0; i < slice_header_extension_length; i++)   slice_header_extension_data_byte[ i ] u(8)  }  byte_alignment( ) } 2.7. Example Sequence Parameter Set

seq_parameter_set_rbsp( ) { Descriptor  sps_decoding_parameter_set_id u(4)  sps_video_parameter_set_id u(4)  sps_max_sub_layers_minus1 u(3)  sps_reserved_zero_5bits u(5)  profile_tier_level(sps_max_sub_layers_minus1 )  gdr_enabled_flag u(1)  sps_seq_parameter_set_id ue(v)  chroma_format_idc ue(v)  if( chroma_format_idc = = 3 )   separate_colour_plane_flag u(1)  pic_width_max_in_luma_samples ue(v)  pic_height_max_in_luma_samples ue(v)  subpics_present_flag u(1)  if( subpics_present_flag) {   max_subpics_minus1 u(8)   subpic_grid_col_width_minus1 u(v)   subpic_grid_row_height_minus1 u(v)   for(i = 0; i < NumSubPicGridRows; i++ )    for(j = 0; j < NumSubPicGridCols; j++ )     subpic_grid_idx[ i ][ j ] u(v)   for(i = 0; i <= NumSubPics; i++ ) {    subpic_treated_as_pic_flag[ i ] u(1)    loop_filter_across_subpic_enabled_flag[ i ] u(1)   }  }  bit_depth_luma_minus8 ue(v)  bit_depth_chroma_minus8 ue(v)  min_qp_prime_ts_minus4 ue(v)  log2_max_pic_order_cnt_lsb_minus4 ue(v)  if( sps_max_sub_layers_minus1 > 0 )   sps_sub_layer_ordering_info_present_flag u(1)  for( i = ( sps_sub_layer_ordering_info_present_flag ? 0 : sps_max_sub_layers_minus1 );   i <= sps_max_sub_layers_minus1 ; i++ ) {   sps_max_dec_pic_buffering_minus1[ i ] ue(v)   sps_max_num_reorder_pics[ i ] ue(v)   sps_max_latency_increase_plus1[ i ] ue(v)  }  long_term_ref_pics_flag u(1)  inter_layer_ref_pics_present_flag u(1)  sps_idr_rpl_present_flag u(1)  rpl1_same_as_rpl0_flag u(1)  for(i = 0; i < !rpll_same_as_rpl0_flag ? 2 : 1 ; i++ ) {   num_ref_pic_lists_in_sps[ i ] ue(v)   for(j = 0; j < num_ref_pic_lists_in_sps[ i ]; j++)    ref_pic_list_struct(i, j )  }  if(ChromaArrayType != 0 )   qtbtt_dual_tree_intra_flag u(1)  1og2_ctu_size_minus5 u(2)  1og2_min_luma_coding_block_size_minus2 ue(v)  partition_constraints_override_enabled_flag u(1)  sps_1og2_diff_min_qt_min_cb_intra_slice_luma ue(v)  sps_1og2_diff_min_qt_min_cb_inter_slice ue(v)  sps_max_mtt_hierarchy_depth_inter_slice ue(v)  sps_max_mtt_hierarchy_depth_intra_slice_luma ue(v)  if( sps_max_mtt_hierarchy_depth_intra_slice_luma != 0 ) {   sps_log2_diff_max_bt_min_qt_intra_slice_luma ue(v)   sps_log2_diff_max_tt_min_qt_intra_slice_luma ue(v)  }  if( sps_max_mtt_hierarchy_depth_inter_slices != 0 ) {   sps_log2_diff_max_bt_min_qt_inter_slice ue(v)   sps_log2_diff_max_tt_min_qt_inter_slice ue(v)  }  if( qtbtt_dual_tree_intra_flag) {   sps_log2_diff_min_qt_min_cb_intra_slice_chroma ue(v)   sps_max_mtt_hierarchy_depth_intra_slice_chroma ue(v)   if ( sps_max_mtt_hierarchy_depth_intra_slice_chroma != 0 ) {    sps_log2_diff_max_bt_min_qt_intra_slice_chroma ue(v)    sps_log2_diff_max_tt_min_qt_intra_slice_chroma ue(v)   }  }  sps_max_luma_transform_size_64_flag u(1)  if( ChromaArrayType != 0 ) {   same_qp_table_for_chroma u(1)   for(i = 0; i < same_qp_table_for_chroma ? 1: 3 ; i++ ) {    num_points_in_qp_table_minus1[ i ] ue(v)    for(j = 0; j <= num_points_in_qp_table_minus1 [ i ]; j++ ) {     delta_qp_in_val_minus1 [ i ][ j ] ue(v)     delta_qp_out_val[ i ][ j ] ue(v)    }   }  }  sps_weighted_pred_flag u(1)  sps_weighted_bipred_flag u(1)  sps_sao_enabled_flag u(1)  sps_alf_enabled_flag u(1)  sps_transform_skip_enabled_flag u(1)  if( sps_transform_skip_enabled_flag )   sps_bdpcm_enabled_flag u(1)  sps_joint_cbcr_enabled_flag u(1)  sps_ref_wraparound_enabled_flag u(1)  if( sps_ref_wraparound_enabled_flag )   sps_ref_wraparound_offset_minus1 ue(v)  sps_temporal_mvp_enabled_flag u(1)  if( sps_temporal_mvp_enabled_flag )   sps_sbtmvp_enabled_flag u(1)  sps_amvr_enabled_flag u(1)  sps_bdof_enabled_flag u(1)  sps_smvd_enabled_flag u(1)  sps_dmvr_enabled_flag u(1)  if( sps_bdof_enabled_flag | | sps_dmvr_enabled_flag)   sps_bdof_dmvr_slice_present_flag u(1)  sps_mmvd_enabled_flag u(1)  sps_isp_enabled_flag u(1)  sps_mrl_enabled_flag u(1)  sps_mip_enabled_flag u(1)  if( ChromaArrayType != 0 )   sps_cclm_enabled_flag u(1)   if( sps_cclm_enabled_flag && chroma_format_idc = = 1 )   sps_cclm_colocated_chroma_flag u(1)  sps_mts_enabled_flag u(1)  if( sps_mts_enabled_flag ) {   sps_explicit_mts_intra_enabled_flag u(1)   sps_explicit_mts_inter_enabled_flag u(1)  }  sps_sbt_enabled_flag u(1)  if( sps_sbt_enabled_flag )   sps_sbt_max_size_64_flag u(1)  sps_affine_enabled_flag u(1)  if( sps_affine_enabled_flag ) {   sps_affine_type_flag u(1)   sps_affine_amvr_enabled_flag u(1)   sps_affine_prof_enabled_flag u(1)  }  if( chroma_format_idc = = 3 )   sps_palette_enabled_flag u(1)  sps_bcw_enabled_flag u(1)  sps_ibc_enabled_flag u(1)  sps_ciip_enabled_flag u(1)  if( sps_mmvd_enabled_flag )   sps_fpel_mmvd_enabled_flag u(1)  sps_triangle_enabled_flag u(1)  sps_lmcs_enabled_flag u(1)  sps_lfnst_enabled flag u(1)  sps_ladf_enabled_flag u(1)  if ( sps_ladf_enabled_flag ) {   sps_num_ladf_intervals_minus2 u(2)   sps_ladf_lowest_interval_qp_offset se (v)   for(i = 0; i < sps_num_ladf_intervals_minus2 + 1 ; i++ ) {    sps_ladf_qp_offset[ i ] se (v)    sps_ladf_delta_threshold_minus1 [ i ] ue (v)   }  }  sps_scaling_list_enabled_flag u(1)  hrd_parameters_present_flag u(1)  if( general_hrd_parameters_present_flag ) {   num_units_in_tick u(32)   time_scale u(32)   sub_layer_cpb_parameters_present_flag u(1)   if( sub_layer_cpb_parameters_present_flag )    general_hrd_parameters(0, sps_max_sub_layers_minus1 )   else    general_hrd_parameters( sps_max_sub_layers_minus1, sps_max_sub_layers_minus1 )  }  vui_parameters_present_flag u(1)  if( vui_parameters_present_flag )   vui_parameters( )  sps_extension_flag u(1)  if( sps_extension_flag )   while( more_rbsp_data( ) )   sps_extension_data_flag u(1)  rbsp_trailing_bits( ) } 2.8 Example Picture Parameter Set

pic_parameter_set_rbsp( ) { Descriptor  pps_pic_parameter_set_id ue(v)  pps_seq_parameter_set_id ue(v)  pic_width_in_luma_samples ue(v)  pic_height_in_luma_samples ue(v)  conformance_window_flag u(1)  if( conformance_window_flag ) {   conf_win_left_offset ue(v)   conf_win_right_offset ue(v)   conf_win_top_offset ue(v)   conf_win_bottom_offset ue(v)  }  output_flag_present_flag u(1)  single_tile_in_pic_flag u(1)  if( !single_tile_in_pic_flag ) {   uniform_tile_spacing_flag u(1)   if( uniform_tile_spacing_flag ) {    tile_cols_width_minus1 ue(v)    tile_rows_height_minus1 ue(v)   } else {    num_tile_columns_minus1 ue(v)    num_tile_rows_minus1 ue(v)    for(i = 0; i < num_file_columns_minus1; i++ )     tile_column_width_minus1[ i ] ue(v)    for(i = 0; i < num_tile_rows_minus1; i++ )     tile_row_height_minus1[ i ] ue(v)   }   brick_splitting_present_flag u(1)   if( uniform_tile_spacing_flag && brick_splitting_present_flag )    num_tiles_in_pic_minus1 ue(v)   for(i = 0; brick_splitting_present_flag && i <= num_tiles_in_pic_minus1 + 1; i++ ) {    if( RowHeight[ i ] > 1 )     brick_split_flag[ i ] u(1)    if( brick_split_flag[ i ] ) {     if( RowHeight[ i ] > 2 )      uniform_brick_spacing_flag[ i ] u(1)     if( uniform_brick_spacing_flag[ i ] )      brick_height_minus1[ i ] ue(v)     else {      num_brick_rows_minus2[ i ] ue(v)     for(j = 0; j <= num_brick_rows_minus2[ i ]; j++ )      brick_row_height_minus1[ i ][ j ] ue(v)     }    }   }   single_brick_per_slice_flag u(1)   if( !single_brick_per_slice_flag )    rect_slice_flag u(1)   if( rect_slice_flag && !single_brick_per_slice_flag ) {    num_slices_in_pic_minus1 ue(v)    bottom_right_brick_idx_length_minus1 ue(v)    for(i = 0; i < num_slices_in_pic_minus1; i++ ) {     bottom_right_brick_idx_delta[ i ] u(v)     brick_idx_delta_sign_flag[ i ] u(1)    }   }   loop_filler_across_bricks_enabled_flag u(1)   if( loop_filter_across_bricks_enabled_flag )   loop_filler_across_slices_enabled_flag u(1)  }  if( rect_slice_flag) {   signalled_slice_id_flag u(1)   if( signalled_slice_id_flag ) {    signalled_slice_id_length_minus1 ue(v)    for(i = 0; i <= num_slices_in_pic_minus1; i++ )     slice_id[ i ] u(v)   }  }  entropy_coding_sync_enabled_flag u(1)  if( !single_tile_in_pic_flag | | entropy_coding_sync_enabled_flag )   entry_point_offsets_present_flag u(1)  cabac_init_present_flag u(1)  for(i = 0; i < 2; i++ )   num_ref_idx_default_active_minus1[ i ] ue(v)  rpl1_idx_present_flag u(1)  init_qp_minus26 se(v)  if( sps_transform_skip_enabled_flag )   log2_transform_skip_max_size_minus2 ue(v)  cu_qp_delta_enabled_flag u(1)  if( cu_qp_delta_enabled_flag )   cu_qp_delta_subdiv ue(v)  pps_cb_qp_offset se(v)  pps_cr_qp_offset se(v)  pps_joint_cbcr_qp_offset se(v)  pps_slice_chroma_qp_offsets_present_flag u(1)  cu_chroma_qp_offset_enabled_flag u(1)  if( cu_chroma_qp_offset_enabled_flag ) {   cu_chroma_qp_offset_subdiv ue(v)   chroma_qp_offset_list_len_minus1 ue(v)   for(i = 0; i <= chroma_qp_offset_list_len_minus1; i++ ) {    cb_qp_offset_list[ i ] se(v)    cr_qp_offset_list[ i ] se(v)    joint_cbcr_qp_offset_list[ i ] se(v)   }  }  pps_weighted_pred_flag u(1)  pps_weighted_bipred_flag u(1)  deblocking_filter_control_present_flag u(1)  if( deblocking_filter_control_present_flag ) {   deblocking_filter_override_enabled_flag u(1)   pps_deblocking_filter_disabled_flag u(1)   if( !pps_deblocking_filter_disabled_flag ) {    pps_beta_offset_div2 se(v)    pps_tc_offset_div2 se(v)   }  }  constant_slice_header_params_enabled_flag u(1)  if( constant_slice_header_params_enabled_flag ) {   pps_dep_quant_enabled_idc u(2)   for(i = 0; i < 2; i++ )    pps_ref_pic_list_sps_idc[ i ] u(2)   pps_temporal_mvp_enabled_idc u(2)   pps_mvd_l1_zero_idc u(2)   pps_collocated_from_l0_idc u(2)   pps_six_minus_max_num_merge_cand_plus1 ue(v)   pps_five_minus_max_num_subblock_merge_cand_plus1 ue(v)   pps_max_num_merge_cand_minus_max_num_triangle_cand_minus1 ue(v)  }  pps_loop_filter_across_virtual_boundaries_disabled_flag u(1)  if( pps_loop_filter_across_virtual_boundaries_disabled_flag ) {   pps_num_ver_virtual_boundaries u(2)   for(i = 0; i < pps_num_ver_virtual_boundaries; i++ )    pps_virtual_boundaries_pos_x[ i ] u(13)   pps_num_hor_virtual_boundaries u(2)   for(i = 0; i < pps_num_hor_virtual_boundaries; i++ )    pps_virtual_boundaries_pos_y[ i ] u(13)  }  slice_header_extension_present_flag u(1)  pps_extension_flag u(1)  if( pps_extension_flag )   while( more_rbsp_data( ) )    pps_extension_data_flag u(1)  rbsp_trailing_bits( ) } 2.9. Example Adaptive Parameter Set

adaptation_parameter_set_rbsp( ) { Descriptor  adaptation_parameter_set_id u(5)  aps_params_type u(3)  if( aps_params_type = = ALF_APS )   alf_data( )  else if( aps_params_type = = LMCS_APS )   lmcs_data( )  else if( aps_params_type = = SCALING_APS )   scaling_list_data( )  aps_extension_flag u(1)  if( aps_extension_flag )   while( more_rbsp_data( ) )    aps_extension_data_flag u(1)  rbsp_trailing_bits( ) } alf_data( ) { Descriptor  alf_luma_filter_signal_flag u(1)  alf_chroma_filter_signal_flag u(1)  if( alf_luma_filter_signal_flag ) {   alf_luma_clip_flag u(1)   alf_luma_num_filters_signalled_minus1 ue(v)   if( alf_luma_num_filters_signalled_minus1 > 0 ) {    for( filtIdx = 0; filtIdx < NumAlfFilters; filtIdx++ )     alf_luma_coeff_delta_idx[ filtIdx ] u(v)   }   alf_luma_coeff_signalled_flag u(1)   if( alf_luma_coeff_signalled_flag ) {    for( sfIdx = 0; sfIdx <= alf_luma_num_filters_signalled_minus1 ; sfIdx++ )     alf_luma_coeff_flag[ sfIdx ] u(1)   }   for( sfIdx = 0; sfIdx <= alf_luma_num_filters_signalled_minus1 ; sfIdx++ ) {    if( alf_luma_coeff_flag[ sfIdx ] ) {     for(j = 0; j < 12; j++ ) {      alf_luma_coeff_abs[ sfIdx ][ j ] uek(v)      if( alf_luma_coeff abs[ sfIdx ][ j ] )       alf_luma_coeff_sign[ sfIdx ][ j ] u(1)     }    }   }   if( alf_luma_clip_flag ) {    for( sfIdx = 0; sfIdx <= alf_luma_num_filters_signalled_minus1; sfIdx++ ) {     if( alf_luma_coeff_flag[ sfIdx ] ) {      for(j = 0; j < 12; j++ )       alf_luma_clip_idx[ sfIdx ][ j ] u(2)     }    }   }  }  if( alf_chroma_filter_signal_flag ) {   alf_chroma_num_alt_filters_minus1 ue(v)    for( altIdx = 0; altIdx <= alf_chroma_num_alt_filters_minus1; altIdx++ ) {    alf_chroma_clip_flag[ altIdx ] u(1)    for(j = 0; j < 6; j++ ) {     alf_chroma_coeff_abs[ altIdx ][ j ] uek(v)     if( alf_chroma_coeff_abs[ altIdx ][ j ] > 0 )      alf_chroma_coeff_sign[ altIdx ][ j ] u(1)    }    if( alf_chroma_clip_flag[ altIdx ] ) {     for(j = 0; j < 6; j++ )      alf_chroma_clip_idx[ altIdx ][ j ] u(2)    }   }  } } lmcs_data ( ) { Descriptor  lmcs_min_bin_idx ue(v)  lmcs_delta_max_bin_idx ue(v)  lmcs_delta_cw_prec_minus1 ue(v)  for ( i = lmcs_min_bin_idx; i <= LmcsMaxBinIdx; i++ ) {   lmcs_delta_abs_cw[ i ] u(v)   if ( lmcs_delta_abs_cw[ i ] ) > 0 )    lmcs_delta_sign_cw_flag[ i ] u(1)  } } scaling_list_data( ) { Descriptor  for( sizeId = 1; sizeId < 7; sizeId++ )   for( matrixId = 0; matrixId < 6; matrixId++ ) {    if( ! ( ( ( sizeId = = 1 ) && (matrixId%3 = = 0 ) ) | |     ( ( sizeId = = 6) && (matrixId%3 != 0 ) ) ) ) {     scaling_list_pred_mode_flag[ sizeId ][ matrixId ] u(1)     if( !scaling_list_pred_mode_flag[ sizeId ][ matrixId ] )      scaling_list_pred_matrix_id_delta[ sizeId ][ matrixId ] ue(v)     else {      nextCoef = 8      coefNum = Min(64, (1 << (sizeId << 1 ) ) )      if( sizeId > 3 ) {       scaling_list_dc_coef_minus8[ sizeId − 4 ][ matrixId ] se(v)       nextCoef = scaling_list_dc_coef_minus8[ sizeId − 4 ][ matrixId ] + 8      }      for(i = 0; i < coefNum; i++ ) {       x = DiagScanOrder[ 3 ][ 3 ][ i ][ 0 ]       y = DiagScanOrder[ 3 ][ 3 ][ i ][ 1 ]       if ( !( sizeId = = 6 && x >= 4 && y >= 4) ) {        scaling_list_delta_coef se(v)        nextCoef = ( nextCoef + scaling_list_delta_coef + 256 ) % 256        ScalingList[ sizeId ][ matrixId [ i ] = nextCoef       }      }     }    }   }  } } 2.10. Example Picture Header

In some embodiments, the picture header is designed to have the following properties:

1. Temporal Id and layer Id of picture header NAL unit are the same as temporal Id and layer Id of layer access unit that contains the picture header.

2. Picture header NAL unit shall precede NAL unit containing the first slice of its associated picture. This established the association between a picture header and slices of picture associated with the picture header without the need of having picture header Id signalled in picture header and referred to from slice header.

3. Picture header NAL unit shall follow picture level parameter sets or higher level such as DPS, VPS, SPS, PPS, etc. This consequently requires those parameter sets to be not repeated/present within a picture or within an access unit.

4. Picture header contains information about picture type of its associated picture. The picture type may be used to define the following (not an exhaustive list)

-   -   a. The picture is an IDR picture     -   b. The picture is a CRA picture     -   c. The picture is a GDR picture     -   d. The picture is a non-IRAP, non-GDR picture and contains         I-slices only     -   e. The picture is a non-IRAP, non-GDR picture and may contain P-         and I-slices only     -   f. The picture is a non-IRAP, non-GDR picture and contains any         of B-, P-, and/or I-slices

5. Move signalling of picture level syntax elements in slice header to picture header.

6. Signal non-picture level syntax elements in slice header that are typically the same for all slices of the same picture in picture header. When those syntax elements are not present in picture header, they may be signalled in slice header.

In some implementations, a mandatory picture header concept is used to be transmitted once per picture as the first VCL NAL unit of a picture. It is also proposed to move syntax elements currently in the slice header to this picture header. Syntax elements that functionally only need to be transmitted once per picture could be moved to the picture header instead of being transmitted multiple times for a given picture, e.g., syntax elements in the slice header are transmitted once per slice. Moving slice header syntax elements constrained to be the same within a picture

The syntax elements are already constrained to be the same in all slices of a picture. It is asserted that moving these fields to the picture header so they are signalled only once per picture instead of once per slice avoids unnecessary redundant transmission of bits without any change to the functionality of these syntax elements.

1. In some implementations, there is the following semantic constraint:

When present, the value of each of the slice header syntax elements slice_pic_parameter_set_id, non_reference_picture_flag, colour_plane_id, slice_pic_order_cnt_lsb, recovery_poc_cnt, no_output_of_prior_pics_flag, pic_output_flag, and slice_temporal_mvp_enabled_flag shall be the same in all slice headers of a coded picture. Thus each of these syntax elements could be moved to the picture header to avoid unnecessary redundant bits.

The recovery_poc_cnt and no_output_of_prior_pics_flag are not moved to the picture header in this contribution. Their presence in the slice header is dependent on a conditional check of the slice header nal_unit_type, so they are suggested to be studied if there is a desire to move these syntax elements to the picture header.

2. In some implementations, there are the following semantic constraints:

When present, the value of slice_lmcs_aps_id shall be the same for all slices of a picture.

When present, the value of slice_scaling_list_aps_id shall be the same for all slices of a picture. Thus each of these syntax elements could be moved to the picture header to avoid unnecessary redundant bits.

In some embodiments, the syntax elements are not currently constrained to be the same in all slices of a picture. It is suggested to assess the anticipated usage of these syntax elements to determine which can be moved into the picture header to simplify the overall VVC design as it is claimed there is a complexity impact to processing a large number of syntax elements in every slice header.

1. The following syntax elements are proposed to be moved to the picture header. There are currently no restrictions on them having different values for different slices but it is claimed there is no/minimal benefit and coding loss to transmitting them in every slice header as their anticipated usage would change at the picture level:

a. six_minus_max_num_merge_cand

b. five_minus_max_num_subblock_merge_cand

c. slice_fpel_mmvd_enabled_flag

d. slice_disable_bdof_dmvr_flag

e. max_num_merge_cand_minus_max_num_triangle_cand

f. slice_six_minus_max_num_ibc_merge_cand

2. The following syntax elements are proposed to be moved to the picture header. There are currently no restrictions on them having different values for different slices but it is claimed there is no/minimal benefit and coding loss to transmitting them in every slice header as their anticipated usage would change at the picture level:

a. partition_constraints_override_flag

b. slice_log 2_diff_min_qt_min_cb_luma

c. slice_max_mtt_hierarchy_depth_luma

d. slice_log 2_diff_max_bt_min_qt_luma

e. slice_log 2_diff_max_tt_min_qt_luma

f. slice_log 2_diff_min_qt_min_cb_chroma

g. slice_max_mtt_hierarchy_depth_chroma

h. slice_log 2_diff_max_bt_min_qt_chroma

i. slice_log 2_diff_max_tt_min_qt_chroma

The conditional check “slice_type==I” associated with some of these syntax elements has been removed with the move to the picture header.

3. The following syntax elements are proposed to be moved to the picture header. There are currently no restrictions on them having different values for different slices but it is claimed there is no/minimal benefit and coding loss to transmitting them in every slice header as their anticipated usage would change at the picture level:

-   -   a. mvd_l1_zero_flag

The conditional check “slice_type==B” associated with some of these syntax elements has been removed with the move to the picture header.

4. The following syntax elements are proposed to be moved to the picture header. There are currently no restrictions on them having different values for different slices but it is claimed there is no/minimal benefit and coding loss to transmitting them in every slice header as their anticipated usage would change at the picture level:

a. dep_quant_enabled_flag

b. sign_data_hiding_enabled_flag

2.10.1 Example Syntax Tables

7.3.2.8 Picture Header RBSP Syntax

picture_header_rbsp( ) { Descriptor  non_reference_picture_flag u(1)  gdr_pic_flag u(1)  no_output_of_prior_pics_flag u(1)  if( gdr_pic_flag )   recovery_poc_cnt ue(v)  ph_pic_parameter_set_id ue(v)  if( sps_subpic_id_present_flag && !sps_subpic_id_signalling_flag ) {   ph_subpic_id_signalling_present_flag u(1)   if( ph_subpics_id_signalling_present_flag ) {    ph_subpic_id_len_minus1 ue(v)    for(i = 0; i < NumSubPics; i++ )     ph_subpic_id[ i ] u(v)   }  }  if( !sps_loop_filter_across_virtual_boundaries_disabled_present_flag ) {   ph_loop_filter_across_virtual_boundaries_disabled_present_flag u(1)   if(ph_loop_filter_across_virtual_boundaries_disabled_present_flag ) {    ph_num_ver_virtual_boundaries u(2)    for(i = 0; i < ph_num_ver_virtual_boundaries; i++ )     ph_virtual_boundaries_pos_x[ i ] u(13)    ph_num_hor_virtual_boundaries u(2)    for(i = 0; i < ph_num_hor_virtual_boundaries; i++ )     ph_virtual_boundaries_pos_y[ i ] u(13)   }  }  if( separate_colour_plane_flag = = 1 )   colour_plane_id u(2)  if( output_flag_present_flag )   pic_output_flag u(1)  pic_rpl_present_flag u(1)  if( pic_rpl_present_flag) {   for(i = 0; i < 2; i++ ) {    if( num_ref_pic_lists_in_sps[ i ] > 0 && !pps_ref_pic_list_sps_idc[ i ] &&      (i = = 0 | | (i = = 1 && rpl1_idx_present_flag ) ) )     pic_rpl_sps_flag[ i ] u(1)    if( pic_rpl_sps_flag[ i ] ) {     if( num_ref_pic_lists_in_sps[ i ] > 1 &&       (i = = 0 | | (i = = 1 && rpl1_idx_present_flag ) ) )     pic_rpl_idx[ i ] u(v)    } else     ref_pic_list_struct(i, num_ref_pic_lists_in_sps[ i ] )    for(j = 0; j < NumLtrpEntries[ i ][ RplsIdx[ i ] ]; j++ ) {     if(ltrp_in_slice_header_flag[ i ][ RplsIdx[ i ] ] )      pic_poc_lsb_lt[ i ][ j ] u(v)     pic_delta_poc_msb_present_flag[ i ][ j ] u(1)     if( pic_delta_poc_msb_present_flag[ i ][ j ] )      pic_delta_poc_msb_cycle_lt[ i ][ j ] ue(v)    }   }  }  if( partition_constraints_override_enabled_flag ) {   partition_constraints_override_flag ue(v)   if( partition_constraints_override_flag) {    pic_log2_diff_min_qt_min_cb_intra_slice_luma ue(v)    pic_log2_diff_min_qt_min_cb_inter_slice ue(v)    pic_max_mtt_hierarchy_depth_inter_slice ue(v)    pic_max_mtt_hierarchy_depth_intra_slice_luma ue(v)    if( pic_max_mtt_hierarchy_depth_intra_slice_luma !=0 ) {     pic_log2_diff_max_bt_min_qt_intra_slice_luma ue(v)     pic_log2_diff_max_tt_min_qt_intra_slice_luma ue(v)    }    if( pic_max_mtt_hierarchy_depth_inter_slice != 0 ) {     pic_log2_diff_max_bt_min_qt_inter_slice ue(v)     pic_log2_diff_max_tt_min_qt_inter_slice ue(v)    }    if( qtbtt_dual_tree_intra_flag ) {     pic_log2_diff_min_qt_min_cb_intra_slice_chroma ue(v)     pic_max_mtt_hierarchy_depth_intra_slice_chroma ue(v)     if( pic_max_mtt_hierarchy_depth_intra_slice_chroma != 0 ) {      pic_log2_diff_max_bt_min_qt_intra_slice_chroma ue(v)      pic_log2_diff_max_tt_min_qt_intra_slice_chroma ue(v)     }    }   }  }  if( cu_qp_delta_enabled_flag ) {   pic_cu_qp_delta_subdiv_intra_slice ue(v)   pic_cu_qp_delta_subdiv_inter_slice ue(v)  }  if( cu_chroma_qp_offset_enabled_flag ) {   pic_cu_chroma_qp_offset_subdiv_intra_slice ue(v)   pic_cu_chroma_qp_offset_subdiv_inter_slice ue(v)  }  if( sps_temporal_mvp_enabled_flag && !pps_temporal_mvp_enabled_idc )   pic_temporal_mvp_enabled_flag u(1)  if(!pps_mvd_l1_zero_idc)   mvd_l1_zero_flag u(1)  if( !pps_six_minus_max_num_merge_cand_plus1 )   pic_six_minus_max_num_merge_cand ue(v)  if( sps_affine_enabled_flag &&    !pps_five_minus_max_num_subblock_merge_cand_plus1 )   pic_five_minus_max_num_subblock_merge_cand ue(v)  if( sps_fpel_mmvd_enabled_flag )   pic_fpel_mmvd_enabled_flag u(1)  if( sps_bdof_dmvr_slice_present_flag )   pic_disable_bdof_dmvr_flag u(1)  if( sps_triangle_enabled_flag&& MaxNumMergeCand >= 2 &&    !pps_max_num_merge_cand_minus_max_num_triangle_cand_minus1 )   pic_max_num_merge_cand_minus_max_num_triangle_cand ue(v)  if ( sps_ibc_enabled_flag )   pic_six_minus_max_num_ibc_merge_cand ue(v)  if( sps_joint_cbcr_enabled_flag )   pic_joint_cbcr_sign_flag u(1)  if( sps_sao_enabled_flag ) {   pic_sao_enabled_present_flag u(1)   if( pic_sao_enabled_present_flag ) {    pic_sao_luma_enabled_flag u(1)    if(ChromaArrayType != 0 )     pic_sao_chroma_enabled_flag u(1)   }  }  if( sps_alf_enabled_flag ) {   pic_alf_enabled_present_flag u(1)   if( pic_alf_enabled_present_flag ) {    pic_alf_enabled_flag u(1)    if( pic_alf_enabled_flag ) {     pic_num_alf_aps_ids_luma u(3)     for(i = 0; i < pic_num_alf_aps_ids_luma; i++ )      pic_alf_aps_id_luma[ i ] u(3)     if(ChromaArrayType != 0 )      pic_alf_chroma_idc u(2)     if( pic_alf_chroma_idc )      pic_alf_aps_id_chroma u(3)    }   }  }  if ( !pps_dep_quant_enabled_flag )   pic_dep_quant_enabled_flag u(1)  if( !pic_dep_quant_enabled_flag )   sign_data_hiding_enabled_flag u(1)  if( deblocking_filter_override_enabled_flag ) {   pic_deblocking_filter_override_present_flag u(1)   if( pic_deblocking_filter_override_present_flag ) {    pic_deblocking_filter_override_flag u(1)    if( pic_deblocking_filter_override_flag ) {     pic_deblocking_filter_disabled_flag u(1)     if( !pic_deblocking_filter_disabled_flag ) {      pic_beta_offset_div2 se(v)      pic_tc_offset_div2 se(v)     }    }   }  }  if( sps_lmcs_enabled_flag ) {   pic_lmcs_enabled_flag u(1)   if( pic_lmcs_enabled_flag ) {    pic_lmcs_aps_id u(2)    if(ChromaArrayType != 0 )     pic_chroma_residual_scale_flag u(1)   }  }  if( sps_scaling_list_enabled_flag ) {   pic_scaling_list_present_flag u(1)   if( pic_scaling_list_present_flag )    pic_scaling_list_aps_id u(3)  }  if( picture_header_extension_present_flag ) {   ph_extension_length ue(v)   for(i = 0; i < ph_extension_length; i++)    ph_extension_data_byte[ i ] u(8)  }  rbsp_trailing_bits( ) } 2.11. Example DMVR

Decoder-side Motion Vector Refinement (DMVR) utilizes the bilateral matching (BM) to derive motion information of the current CU by finding the closest match between two blocks along the motion trajectory of the current CU in two different reference pictures. The BM method calculates the distortion between the two candidate blocks in the reference picture list L0 and list L1. As illustrated in FIG. 1 , the SAD between the red blocks based on each MV candidate around the initial MV is calculated. The MV candidate with the lowest SAD becomes the refined MV and used to generate the bi-predicted signal. The cost function used in the matching process is row-subsampled SAD (sum of absolute difference). An example in FIG. 7 .

In VTM5.0, DMVR is adopted to refine motion vectors (MVs) at the decoder for a coding unit (CU) when the CU is coded with regular merge/skip mode and bi-prediction, one reference picture is before the current picture and the other reference picture is after the current picture in display order, the temporal distance between the current picture and one reference picture is equal to that between the current picture and the other reference picture, and the bi-prediction with CU weights (BCW) selects equal weights. When DMVR is applied, one luma coding block (CB) is divided into several independently processed subblocks of size min(cbWidth, 16)×min(cbHeight, 16). DMVR refines MVs of each subblock by minimizing the SAD between ½-subsampled 10-bitL0 and L1 prediction samples generated by bilinear interpolation. For each subblock, integer ΔMV search around the initial MVs (i.e., the MVs of the selected regular merge/skip candidate) is first performed using SAD, and then fractional ΔMV derivation is performed to obtain the final MVs.

BDOF refines the luma prediction samples for a CU when the CU is coded with bi-prediction, one reference picture is before the current picture and the other reference picture is after the current picture in display order, and BCW selects equal weights. The eight-tap interpolation is used for generating the initial L0 and L1 prediction samples according to the input MVs (e.g., final MVs of DMVR in case of enabling DMVR). Next, a two-level early termination process is performed. The first early termination is at subblock level, and the second early termination is at 4×4 block level and is checked when the first early termination does not occur. At each level, the SAD between full-sampled 14-bit L0 and L1 prediction samples in each subblock/4×4 block is calculated first. If the SAD is smaller than one threshold, BDOF is not applied to the subblock/4×4 block. Otherwise, BDOF parameters are derived and used to generate the final luma sample predictors for each 4×4 block. In BDOF, the subblock size is the same as that in DMVR, i.e., min(cbWidth, 16)×min(cbHeight, 16).

When the CU is coded with regular merge/skip mode, one reference picture is before the current picture and the other reference picture is after the current picture in display order, the temporal distance between the current picture and one reference picture is equal to that between the current picture and the other reference picture, and BCW selects equal weights, DMVR and BDOF are both applied. The flow of cascading DMVR and BDOF processes is shown in FIG. 8 .

FIG. 8 shows the flow of cascading DMVR and BDOF processes in VTM5.0. The DMVR SAD operations and BDOF SAD operations are different and not shared.

In order to reduce the latency and operations in this critical path, when DMVR and BDOF are both applied, the latest VVC working draft has been revised to reuse the subblock SAD calculated in DMVR for the subblock early termination in BDOF.

The SAD calculation is defined as follows:

${sad} = {\sum\limits_{x = 0}^{{nSbW} - 1}{\sum\limits_{y = 0}^{{{nSbH}/2} - 1}{{abs}{\quad\left( {{{pL}\;{{0\left\lbrack {x + 2 + {dX}} \right\rbrack}\left\lbrack {{2*y} + 2 + {dY}} \right\rbrack}} - {{pL}\;{{1\left\lbrack {x + 2 - {dX}} \right\rbrack}\left\lbrack {{2*y} + 2 - {dY}} \right\rbrack}}} \right)}}}}$

wherein two variables nSbW and nSbH specifying the width and the height of the current subblock, two (nSbW+4)×(nSbH+4) arrays pL0 and pL1 containing the predicted samples for L0 and L1 respectively, and the integer sample offset (dX, dY) in prediction list L0.

To reduce the penalty of the uncertainty of DMVR refinement, it is proposed to favor the original MV during the DMVR process. The SAD between the reference blocks referred by the initial (or called original) MV candidate is decreased by ¼ of the SAD value. That is, when both dX and dY in above equation are equal to 0, the value of sad is modified as follows: sad=sad−(sad>>2)

When the SAD value is smaller than a threshold (2*subblock width*subblock height), there is no need to perform BDOF anymore.

3. Drawbacks of Existing Implementations

DMVR and BIO do not involve the original signal during refining the motion vectors, which may result in coding blocks with inaccurate motion information. Also, DMVR and BIO sometimes employ the fractional motion vectors after the motion refinements while screen videos usually have integer motion vectors, which makes the current motion information more inaccurate and make the coding performance worse.

When RPR is applied in VVC, RPR (ARC) may have the following problems:

1. With RPR, the interpolation filters may be different for adjacent samples in a block, which is undesirable in SIMD (Single Instruction Multiple Data) implementation.

2. The bounding region does not consider RPR.

3. It is noted that “The conformance cropping window offset parameters are only applied at the output. All internal decoding processes are applied to the uncropped picture size.” However, those parameters may be used in the decoding process when RPR is applied.

4. When deriving the reference sample position, RPR only considers the ratio between two conformance windows. But the top-left offset difference between two conformance windows should also be considered.

5. The ratio between the width/height of a reference picture and that of the current picture is constrained in VVC. However, the ratio between the width/height of the conformance window of a reference picture and that of the conformance window of the current picture is not constrained.

6. Not all the syntax elements are handled properly in the picture header.

7. In current VVC, for TPM, GEO prediction mode, the chroma blending weights are derived regardless of the chroma sample location type of a video sequence. For example, in TPM/GEO, if chroma weights are derived from luma weights, the luma weights may be needed to be downsampled to match the sampling of the chroma signal. The chroma downsampling are normally applied assumes the chroma sample location type 0, which is widely used in ITU-R BT.601 or ITU-R BT.709 container. However, if a different chroma sample location type is used, this could result in a misalignment between the chroma samples and the downsampled Luma samples, which may reduce the coding performance.

8. It is noted that the SAD calculation/SAD threshold doesn't consider the bit-depth impact. Therefore, for higher bit-depth (e.g., 14 or 16 bits input sequences), the threshold for the early termination may be too small.

9. For the non-RPR case, AMVR with ½-pel MV precision (i.e., alternative interpolation filter/switchable interpolation filter) is applied with a 6-tap motion compensation filter but 8-tap is applied to other cases (e.g., 1/16-pel). However, for the RPR case, the same interpolation filter is applied to all cases without considering the mv/mvd precision. Therefore, the signaling of 1-pel case (alternative interpolation filter/switchable interpolation filter) is wasting bits.

10. The decision of partition tree splitting is allowed or not is dependent on the coded picture resolution instead of output picture resolution.

11. SMVD/MMVD are applied which doesn't consider RPR cases. These methods are based on the assumption that symmetric MVD are applied for two reference pictures. However, when output picture resolution are different, such an assumption is not true.

12. Pairwise merge candidate is generated by averaging two MVs from two merge candidates in the same reference picture list. However, when the two reference pictures associated with two merge candidates are with different resolution, the averaging doesn't make sense.

4. Example Techniques and Embodiments

The detailed embodiments described below should be considered as examples to explain general concepts. These embodiments should not be interpreted narrowly way. Furthermore, these embodiments can be combined in any manner.

The methods described below may be also applicable to other decoder motion information derivation technologies in addition to the DMVR and BIO mentioned below.

A motion vector is denoted by (mv_x, mv_y) wherein mv_x is the horizontal component and mv_y is the vertical component.

In this disclosure, the resolution (or dimensions, or width/height, or size) of a picture may refer to the resolution (or dimensions, or width/height, or size) of the coded/decoded picture, or may refer to the resolution (or dimensions, or width/height, or size) of the conformance window in the coded/decoded picture. In one example, the resolution (or dimensions, or width/height, or size) of a picture may refer to that parameters that related to RPR (reference picture resampling) process, such as the scaling window/phase offset window. In one example, the resolution (or dimensions, or width/height, or size) of a picture is related to that associated with the output picture.

Motion compensation in RPR

-   -   1. When the resolution of the reference picture is different to         the current picture, or when the width and/or height of the         reference picture is larger that of the current picture,         predicted values for a group of samples (at least two samples)         of a current block may be generated with the same horizontal         and/or vertical interpolation filter.         -   a. In one example, the group may comprise all samples in a             region of the block.             -   i. For example, a block may be divided into S M×N                 rectangles not overlapped with each other. Each M×N                 rectangle is a group. In an example as shown in FIG. 2 ,                 a 16×16 block can be divided into 16 4×4 rectangles,                 each of which is a group.             -   ii. For example, a row with N samples is a group. N is                 an integer no larger than the block width. In one                 example, N is 4 or 8 or the block width.             -   iii. For example, a column with N samples is a group. N                 is an integer no larger than the block height. In one                 example, N is 4 or 8 or the block height.             -   iv. M and/or N may be pre-defined or derived on-the-fly,                 such as based on block dimension/coded information or                 signaled.         -   b. In one example, samples in the group may have the same MV             (denoted as shared MV).         -   c. In one example, samples in the group may have MVs with             the same horizontal component (denoted as shared horizontal             component).         -   d. In one example, samples in the group may have MVs with             the same vertical component (denoted as shared vertical             component).         -   e. In one example, samples in the group may have MVs with             the same fractional part of the horizontal component             (denoted as shared fractional horizontal component).             -   i. For example, suppose the MV fora first sample is                 (MV1x, MV1y) and the MV for a second sample is (MV2x,                 MV2y), it should be satisfied that MV1x & (2^(M)−1) is                 equal to MV2x & (2^(M)−1), where M denotes MV precision.                 For example, M=4.         -   f. In one example, samples in the group may have MVs with             the same fractional part of the vertical component (denoted             as shared fractional vertical component).             -   i. For example, suppose the MV fora first sample is                 (MV1x, MV1y) and the MV for a second sample is (MV2x,                 MV2y), it should be satisfied that MV1y & (2^(M)−1) is                 equal to MV2y & (2^(M)−1), where M denotes MV precision.                 For example, M=4.         -   g. In one example, for a sample in the group to be             predicted, the motion vector, denoted by MV_(b), may be             firstly derived according to the resolutions of the current             picture and the reference picture (e.g. (refx_(L), refy_(L))             derived in 8.5.6.3.1 in JVET-02001-v14). Then, MV_(b) may be             further modified (e.g., being rounded/truncated/clipped) to             MV′ to satisfy the requirements such as the above bullets,             and MV′ will be used to derive the prediction sample for the             sample.             -   i. In one example, MV′ has the same integer part as                 MV_(b), and the fractional part of the MV′ is set to be                 the shared fractional horizontal and/or vertical                 component.             -   ii. In one example, MV′ is set to be the one with the                 shared fractional horizontal and/or vertical component,                 and closest to MV_(b).         -   h. The shared motion vector (and/or shared horizontal             component and/or shared vertical component and/or shared             fractional vertical component and/or shared fractional             vertical component) may be set to be the motion vector             (and/or horizontal component and/or vertical component             and/or fractional vertical component and/or fractional             vertical component) of a specific sample in the group.             -   i. For example, the specific sample may be at a corner                 of a rectangle-shaped group, such as “A”, “B’, “C” and                 “D” shown in FIG. 3A.             -   ii. For example, the specific sample may be at a center                 of a rectangle-shaped group, such as “E”, “F’, “G” and                 “H” shown in FIG. 3A.             -   iii. For example, the specific sample may be at an end                 of a row-shaped or column-shaped group, such as “A” and                 “D” shown in FIGS. 3B and 3C.             -   iv. For example, the specific sample may be at a middle                 of a row-shaped or column-shaped group, such as “B” and                 “C” shown in FIGS. 3B and 3C.             -   v. In one example, the motion vector of the specific                 sample may be the MV_(b) mentioned in bullet g.         -   i. The shared motion vector (and/or shared horizontal             component and/or shared vertical component and/or shared             fractional vertical component and/or shared fractional             vertical component) may be set to be the motion vector             (and/or horizontal component and/or vertical component             and/or fractional vertical component and/or fractional             vertical component) of a virtual sample located at a             different position compared to all samples in this group.             -   i. In one example, the virtual sample is not in the                 group, but it locates in the region covering all samples                 in the group.                 -   1) Alternatively, the virtual sample is located                     outside the region covering all samples in the                     group, e.g., next to the bottom-right position of                     the region.             -   ii. In one example, the MV of a virtual sample is                 derived in the same way as a real sample but with                 different positions.             -   iii. “V” in FIGS. 3A-3C shows three examples of virtual                 samples.         -   j. The shared MV (and/or shared horizontal component and/or             shared vertical component and/or shared fractional vertical             component and/or shared fractional vertical component) may             be set to be a function of MVs (and/or horizontal components             and/or vertical components and/or fractional vertical             components and/or fractional vertical components) of             multiple samples and/or virtual samples.             -   i. For example, the shared MV (and/or shared horizontal                 component and/or shared vertical component and/or shared                 fractional vertical component and/or shared fractional                 vertical component) may be set to be the average of MVs                 (and/or horizontal components and/or vertical components                 and/or fractional vertical components and/or fractional                 vertical components) of all or partial of samples in the                 group, or of sample “E”, “F”, “G”, “H” in FIG. 3A, or of                 sample “E”, “H” in FIG. 3A, or of sample “A”, “B”, “C”,                 “D” in FIG. 3A, or of sample “A”, “D” in FIG. 3A, or of                 sample “B”, “C” in FIG. 3B, or of sample “A”, “D” in                 FIG. 3B, or of sample “B”, “C” in FIG. 3C, or of sample                 “A”, “D” in FIG. 3C,     -   2. It is proposed that only integer MVs are allowed to perform         the motion compensation process to derive the prediction block         of a current block when the resolution of the reference picture         is different to the current picture, or when the width and/or         height of the reference picture is larger that of the current         picture.         -   a. In one example, the decoded motion vectors for samples to             be predicted are rounded to integer MVs before being used.         -   b. In one example, the decoded motion vector for samples to             be predicted are rounded to the integer MV that is closest             to the decoded motion vector.         -   c. In one example, the decoded motion vector for samples to             be predicted are rounded to the integer MV that is closest             to the decoded motion vector in horizontal direction.         -   d. In one example, the decoded motion vector for samples to             be predicted are rounded to the integer MV that is closest             to the decoded motion vector in vertical direction.     -   3. The motion vectors used in the motion compensation process         for samples in a current block (e.g., shared MV/shared         horizontal or vertical or fractional component/MV′ mentioned in         above bullets) may be stored in the decoded picture buffer and         utilized for motion vector prediction of succeeding blocks in         current/different pictures.         -   a. Alternatively, the motion vectors used in the motion             compensation process for samples in a current block (e.g.,             shared MV/shared horizontal or vertical or fractional             component/MV′ mentioned in above bullets) may be disallowed             to be utilized for motion vector prediction of succeeding             blocks in current/different pictures.             -   i. In one example, the decoded motion vectors (e.g.,                 MV_(b) in above bullets) may be utilized for motion                 vector prediction of succeeding blocks in                 current/different pictures.         -   b. In one example, the motion vectors used in the motion             compensation process for samples in a current block may be             utilized in the filtering process (e.g., deblocking             filter/SAO/ALF).             -   i. Alternatively, the decoded motion vectors (e.g.,                 MV_(b) in above bullets) may be utilized in the                 filtering process.         -   c. In one example, such MV may be derived at sub-block level             and may be stored for each sub-block.     -   4. It is proposed that the interpolation filters used in the         motion compensation process to derive the prediction block of a         current block may be selected depending on whether the         resolution of the reference picture is different to the current         picture, or whether the width and/or height of the reference         picture is larger that of the current picture.         -   a. In one example, the interpolation filters with less taps             may be applied when condition A is satisfied, wherein             condition A depends on the dimensions of the current picture             and/or the reference picture.             -   i. In one example, condition A is the resolution of the                 reference picture is different to the current picture.             -   ii. In one example, condition A is the width and/or                 height of the reference picture is larger than that of                 the current picture.             -   iii. In one example, condition A is W1>a*W2 and/or                 H1>b*H2, wherein (W1, H1) represents the width and                 height of the reference picture and (W2, H2) represents                 the width and height of the current picture, a and b are                 two factors, e.g. a=b=1.5.             -   iv. In one example, condition A may also depend on                 whether bi-prediction is used.             -   v. In one example, 1-tap filters are applied. In other                 words, an integer pixel without filtering is output as                 the interpolation result.             -   vi. In one example, bi-linear filters are applied when                 the resolution of the reference picture is different to                 the current picture.             -   vii. In one example, 4-tap filters or 6-tap filters are                 applied when the resolution of the reference picture is                 different to the current picture, or the width and/or                 height of the reference picture is larger than that of                 the current picture.                 -   1) The 6-tap filters may also be used for the affine                     motion compensation.                 -   2) The 4-tap filters may also be used for                     interpolation for chroma samples.         -   b. In one example, padding samples are used to perform             interpolation when the resolution of the reference picture             is different to the current picture, or the width and/or             height of the reference picture is larger that of the             current picture.         -   c. Whether to and/or how to apply the methods disclosed in             bullet 4 may depend on the color components.             -   i. For example, the methods are only applied on the luma                 component.         -   d. Whether to and/or how to apply the methods disclosed in             bullet 4 may depend on the interpolation filtering             direction.             -   i. For example, the methods are only applied on                 horizontal filtering.             -   ii. For example, the methods are only applied on                 vertical filtering.     -   5. It is proposed that a two-stage process for prediction block         generation is applied when the resolution of the reference         picture is different to the current picture, or when the width         and/or height of the reference picture is larger that of the         current picture.         -   a. In the first stage, a virtual reference block is             generated by up-sampling or downsampling a region in the             reference picture depending on width and/or height of the             current picture and the reference picture.         -   b. In the second stage, the prediction samples are generated             from the virtual reference block by applying interpolation             filtering, independent of width and/or height of the current             picture and the reference picture.     -   6. It is proposed that the calculation of top-left coordinate of         the bounding block for reference sample padding (xSbInt_(L),         ySbInt_(L)) as in some embodiments may be derived depending on         width and/or height of the current picture and the reference         picture.         -   a. In one example, the luma locations in full-sample units             are modified as:             xInt_(i)=Clip3(xSbInt_(L)             −Dx,xSbInt_(L)+sbWidth+Ux,xInt_(i)),             yInt_(i)=Clip3(ySbInt_(L)             −Dy,ySbInt_(L)+sbHeight+Uy,yInt_(i)),             -   where Dx and/or Dy and/or Ux and/or Uy may depend on                 width and/or height of the current picture and the                 reference picture.         -   b. In one example, the chroma locations in full-sample units             are modified as:             xInti=Clip3(xSbInt_(C) −Dx,xSbInt_(C)+sbWidth+Ux,xInti)             yInti=Clip3(ySbInt_(C) −Dy,ySbInt_(C)+sbHeight+Uy,yInti)             -   where Dx and/or Dy and/or Ux and/or Uy may depend on                 width and/or height of the current picture and the                 reference picture.     -   7. Instead of storing/using the motion vectors for a block based         on the same reference picture resolution as current picture, it         is proposed to use the real motion vectors with the resolution         difference taken into consideration.         -   a. Alternatively, furthermore, when using the motion vector             to generate the prediction block, there is no need to             further change the motion vector according to the             resolutions of the current picture and the reference picture             (e.g. (refx_(L), refy_(L))).             Interaction Between RPR and Other Coding Tools     -   8. Whether to/how to apply filtering process (e.g., deblocking         filter) may depend on the resolutions of reference pictures         and/or the resolution of the current picture.         -   a. In one example, the boundary strength (BS) settings in             the deblocking filters may take the resolution differences             into consideration in addition to motion vector differences.             -   i. In one example, the scaled motion vector difference                 according to the current and reference pictures'                 resolutions may be used to determine the boundary                 strength.         -   b. In one example, the strength of deblocking filter for a             boundary between block A and block B may be set differently             (e.g., being increased/decreased) if the resolution of at             least one reference picture of block A is different to (or             smaller than or larger than) the resolution of at least one             reference picture of block B compared to the case that same             resolutions are utilized for the two blocks.         -   c. In one example, a boundary between block A and block B is             marked as to be filtered (e.g., BS is set to 2) if the             resolution of at least one reference picture of block A is             different to (or smaller than or larger than) the resolution             of at least one reference picture of block B.         -   d. In one example, the strength of deblocking filter for a             boundary between block A and block B may be set differently             (e.g., being increased/decreased) if the resolution of at             least one reference picture of block A and/or block B is             different to (or smaller than or larger than) the resolution             of the current picture compared to the case same resolution             is utilized of the reference picture and current picture.         -   e. In one example, a boundary between two blocks is marked             to be filtered (e.g., BS is set to 2) if at least one             reference picture of at least one block of the two has a             resolution different to that of the current picture.     -   9. When a sub-picture exists, a conformance bitstream may should         satisfy the reference picture must have the same resolution as         the current picture.         -   a. Alternatively, when a reference picture has a different             resolution to the current picture, there must be no             sub-picture in the current picture.         -   b. Alternatively, for a sub-picture in the current picture,             it is disallowed to use a reference picture that is with             different resolution as the current picture.             -   i. Alternatively, furthermore, the reference picture                 management may be invoked to exclude those reference                 pictures with different resolutions.     -   10. In one example, sub-pictures (e.g., how to split one picture         to multiple sub-pictures) may be defined separately for pictures         with different resolutions.         -   In one example, the corresponding sub-picture in the             reference picture can be derived by scaling and/or             offsetting a sub-picture of the current picture, if the             reference picture has a different resolution to the current             picture.     -   11. PROF (prediction refinement with optical flow) may be         enabled when the reference picture has a resolution different to         that of the current picture.         -   a. In one example, one set of MV (denoted as MV_(g)) may be             generated for a group of samples and may be used for motion             compensation as described in bullet 1. On the other hand, MV             (denoted as MV_(p)) may be derived for each sample, and the             difference (e.g., corresponds to the Δv used in PROF)             between the MV_(p) and MV_(g) together with the gradients             (e.g., spatial gradients of the motion compensated blocks)             may be used for deriving the prediction refinement.         -   b. In one example, MV_(p) may be with a different precision             from MV_(g). For example, MV_(p) may be with 1/N-pel (N>0)             precision, N=32, 64 etc.         -   c. In one example, MV_(g) may be with a different precision             form the internal MV precision (e.g., 1/16-pel).         -   d. In one example, the prediction refinement is added to the             prediction block to generate refined prediction block.         -   e. In one example, such method may be applied in each             prediction direction.         -   f. In one example, such method may be applied only in             uni-prediction case.         -   g. In one example, such method may be applied in             uni-prediction or/and bi-prediction.         -   h. In one example, such method may be applied only when the             reference picture has a different resolution from the             current picture.     -   12. It is proposed that only one MV may be utilized for a         block/sub-block to perform the motion compensation process to         derive the prediction block of a current block when the         resolution of the reference picture is different to that of the         current picture.         -   a. In one example, the only MV for the block/sub-block may             be defined as a function (e.g., average) of all MVs             associated with each sample within the block/sub-block.         -   b. In one example, the only MV for the block/sub-block may             be defined as a selected MV associated with a selected             sample (e.g., center sample) within the block/sub-block.         -   c. In one example, only one MV may be utilized a 4×4 block             or subblock (e.g., 4×1).         -   d. In one example, BIO may be further applied to compensate             the precision loss due to a block-based motion vector.     -   13. A lazy mode without signalling any block-based motion         vectors may be applied when the width and/or height of the         reference picture is different from that of the current picture.         -   a. In one example, no motion vectors may be signaled and the             motion compensation process is to approximate the case of a             pure resolution change of a still image.         -   b. In one example, only a motion vector at             picture/tile/brick/CTU level may be signal and related             blocks may use the motion vector when resolution changes.     -   14. PROF may be applied to approximate motion compensation when         the width and/or height of the reference picture is different to         that of the current picture for blocks coded with affine         prediction mode and/or non-affine prediction mode.         -   a. In one example, PROF may be enabled when the width and/or             height of the reference picture and that of the current             picture are different.         -   b. In one example, a set of affine motions may be generated             by combining the indicated motion and resolution scaling and             used by PROF.     -   15. Interweaved prediction (e.g. as proposed in JVET-K0102) may         be applied to approximate motion compensation when the width         and/or height of the reference picture is different to that of         the current picture.         -   a. In one example, resolution change (zooming) is             represented as an affine motion, and interweaved motion             prediction may be applied.     -   16. LMCS and/or chroma residual scaling may be disabled when the         width and/or height of the current picture is different to that         of the IRAP picture in a same IRAP period.         -   a. In one example, when LMCS is disabled, the slice level             flags such as slice_lmcs_enabled_flag, slice_lmcs_aps_id,             and slice_chroma_residual_scale flag may be not signaled and             inferred to be 0.         -   b. In one example, when chroma residual scaling is disabled,             the slice level flags such as             slice_chroma_residual_scale_flag may be not signaled and             inferred to be 0.             Constrains on RPR     -   17. RPR may be applied to coding blocks with block dimensions         constrains.         -   a. In one example, for an M×N coding block, with M as the             block width and N as the block height, when M*N<T or M*N<=T             (such as T=256), RPR may be not used.         -   b. In one example, when M<K (or M<=K) (such as K=16) and/or             N<L (or N<=L) (such as L=16), RPR may be not used.     -   18. Bitstream conformance may be added to restrict the ratio         between the width and/or height of an active reference picture         (or its conformance window) and that of the current picture (or         its conformance window). Suppose refPicW and refPicH denote the         width and height of reference picture, curPicW and curPicH         denote the width and height of current picture,         -   a. In one example, when (refPicW−curPicW) is equal to an             integer number, the reference picture may be marked as             active reference picture.             -   i. Alternatively, when (refPicW−curPicW) is equal to a                 factional number, the reference picture may be marked as                 not available.         -   b. In one example, when (refPicW−curPicW) is equal to (X*n),             where X denotes a fractional number such as X=½, and n             denotes an integer number such as n=1, 2, 3, 4 . . . , the             reference picture may be marked as active reference picture.             -   i. In one example, when (refPicW−curPicW) is not equal                 to (X*n), the reference picture may be marked as not                 available.     -   19. Whether to and/or how to enable a coding tool (e.g.,         bi-prediction/the whole triangular prediction mode         (TPM)/blending process in TPM) for a M×N block may depend on the         resolutions of reference pictures (or their conformance windows)         and/or that of the current picture (or its conformance window).         -   a. In one example, M*N<T or M*N<=T (such as T=64).         -   b. In one example, M<K (or M<=K) (such as K=16) and/or N<L             (or N<=L) (such as L=16).         -   c. In one example, the coding tool is not allowed when             width/height of at least one reference picture is different             to the current picture,             -   i. In one example, the coding tool is not allowed when                 width/height of at least one reference picture of the                 block is larger that of the current picture.         -   d. In one example, the coding tool is not allowed when             width/height of each reference picture of the block is             different to that of the current picture,             -   i. In one example, the coding tool is not allowed when                 width/height of each reference pictures is larger that                 of the current picture.         -   e. Alternatively, furthermore, when the coding tool is not             allowed, motion compensation may be conducted with one MV as             a uni-prediction.             Conformance Window Related     -   20. The conformance cropping window offset parameters (e.g.,         conf_win_left_offset) are signaled in N-pel precision instead of         1-pel wherein N is an positive integer greater than 1.         -   a. In one example, the actual offset may be derived as the             signaled offset multiplied by N.         -   b. In one example, N is set to 4 or 8.     -   21. It is proposed that the conformance cropping window offset         parameters are not only applied at the output. Certain internal         decoding processes may depend on the cropped picture size (e.g.,         the resolution of a conformance window in a picture).     -   22. It is proposed that the conformance cropping window offset         parameters in a first video unit (e.g. PPS) and in a second         video unit may be different when the width and/or height of a         picture denoted as (pic_width_in_luma_samples,         pic_height_in_luma_samples) in the first video unit and second         video unit are the same.     -   23. It is proposed that the conformance cropping window offset         parameters in a first video unit (e.g. PPS) and in a second         video unit should be the same in a conformance bitstream when         the width and/or height of a picture denoted as         (pic_width_in_luma_samples, pic_height_in_luma_samples) in the         first video unit and second video unit are different.         -   a. It is proposed that the conformance cropping window             offset parameters in a first video unit (e.g. PPS) and in a             second video unit should be the same in a conformance             bitstream no matter the width and/or height of a picture             denoted as (pic_width_in_luma_samples,             pic_height_in_luma_samples) in the first video unit and             second video unit are the same or not.     -   24. Suppose the width and height of the conformance window         defined in a first video unit (e.g. PPS) are denoted as W1 and         H1, respectively. The width and height of the conformance window         defined in a second video unit (e.g. PPS) are denoted as W2 and         H2, respectively. The top-left position of the conformance         window defined in a first video unit (e.g. PPS) are denoted as         X1 and Y1. The top-left position of the conformance window         defined in a second video unit (e.g. PPS) are denoted as X2 and         Y2. The width and height of the coded/decoded picture (e.g.         pic_width_in_luma_samples and pic_height_in_luma_samples)         defined in a first video unit (e.g. PPS) are denoted as PW1 and         PH1, respectively. The width and height of the coded/decoded         picture defined in a second video unit (e.g. PPS) are denoted as         PW2 and PH2.         -   a. In one example, W1/W2 should be equal to X1/X2 in a             conformance bitstream.             -   i. Alternatively, W1/X1 should be equal to W2/X2 in a                 conformance bitstream.             -   ii. Alternatively, W1*X2 should be equal to W2*X1 in a                 conformance bitstream.         -   b. In one example, H1/H2 should be equal to Y1/Y2 in a             conformance bitstream.             -   i. Alternatively, H1/Y1 should be equal to H2/Y2 in a                 conformance bitstream.             -   ii. Alternatively, H1*Y2 should be equal to H2*Y1 in a                 conformance bitstream.         -   c. In one example, PW1/PW2 should be equal to X1/X2 in a             conformance bitstream.             -   i. Alternatively, PW1/X1 should be equal to PW2/X2 in a                 conformance bitstream.             -   ii. Alternatively, PW1*X2 should be equal to PW2*X1 in a                 conformance bitstream.         -   d. In one example, PH1/PH2 should be equal to Y1/Y2 in a             conformance bitstream.             -   i. Alternatively, PH1/Y1 should be equal to PH2/Y2 in a                 conformance bitstream.             -   ii. Alternatively, PH1*Y2 should be equal to PH2*Y1 in a                 conformance bitstream.         -   e. In one example, PW1/PW2 should be equal to W1/W2 in a             conformance bitstream.             -   i. Alternatively, PW1/W1 should be equal to PW2/W2 in a                 conformance bitstream.             -   ii. Alternatively, PW1*W2 should be equal to PW2*W1 in a                 conformance bitstream.         -   f. In one example, PH1/PH2 should be equal to H1/H2 in a             conformance bitstream.             -   i. Alternatively, PH1/H1 should be equal to PH2/H2 in a                 conformance bitstream.             -   ii. Alternatively, PH1*H2 should be equal to PH2*H1 in a                 conformance bitstream.         -   g. In a conformance bitstream, if PW1 is greater than PW2,             W1 must be greater than W2.         -   h. In a conformance bitstream, if PW1 is smaller than PW2,             W1 must be smaller than W2.         -   i. In a conformance bitstream, (PW1−PW2)*(W1−W2) must be no             smaller than 0.         -   j. In a conformance bitstream, if PH1 is greater than PH2,             H1 must be greater than H2.         -   k. In a conformance bitstream, if PH1 is smaller than PH2,             H1 must be smaller than H2.         -   l. In a conformance bitstream, (PH1−PH2)*(H1−H2) must be no             smaller than 0.         -   m. In a conformance bitstream, W1/W2 must be no larger than             (or smaller than) PW1/PW2 if PW1>=PW2.         -   n. In a conformance bitstream, H1/H2 must be no larger than             (or smaller than) PH1/PH2 if PH1>=PH2.     -   25. Suppose the width and height of the conformance window of         the current picture are denoted as W and H, respectively. The         width and height of the conformance window of a reference         picture are denoted as W′ and H′, respectively. Then at least         one constraint below should be followed by a conformance         bit-stream.         -   a. W*pw>=W′; pw is an integer such as 2.         -   b. W*pw>W′; pw is an integer such as 2.         -   c. W′*pw′>=W; pw′ is an integer such as 8.         -   d. W′*pw′>W; pw′ is an integer such as 8.         -   e. H*ph>=H′; ph is an integer such as 2.         -   f. H*ph>H′; ph is an integer such as 2.         -   g. H′*ph′>=H; ph′ is an integer such as 8.         -   h. H′*ph′>H; ph′ is an integer such as 8.         -   i. In one example, pw is equal to pw′.         -   j. In one example, ph is equal to ph′.         -   k. In one example, pw is equal to ph.         -   l. In one example, pw′ is equal to ph′.         -   m. In one example, the above sub-bullets may be required to             be satisfied by a conformance bitstream when W and H             represent the width and height of the current picture,             respectively. W′ and H′ represent the width and height of a             reference picture.     -   26. It is proposed that the conformance window parameters are         partially signaled.         -   a. In one example, the top-left sample in a conformance             window of a picture is the same one as that in the picture.         -   b. For example, conf win left offset as defined in VVC is             not signaled and inferred to be zero.         -   c. For example, conf_win_top_offset as defined in VVC is not             signaled and inferred to be zero.     -   27. It is proposed that the derivation of the position (e.g.         (refx_(L), refy_(L)) as defined in VVC) of a reference sample         may depend on the top-left position (e.g. (conf_win_left_offset,         conf_win_top_offset) as defined in VVC) of the conformance         window of the current picture and/or the reference picture. FIG.         4 shows examples of the samples positions derived as in VVC (a)         and in a proposed method (b). Dashed rectangles represent the         conformance windows.         -   a. In one example, the dependency exists only when the width             and/or the height of the current picture and that of the             reference picture are different.         -   b. In one example, the derivation of the horizontal position             (e.g. refx_(L) as defined in VVC) of a reference sample may             depend on the left position (e.g. conf_win_left_offset as             defined in VVC) of the conformance window of the current             picture and/or the reference picture.             -   i. In one example, the horizontal position (denoted as                 xSb′) of the current sample relative to the top-left                 position of the conformance window in the current                 picture is calculated and used to derive the position of                 the reference sample.                 -   1) For example,                     xSb′=xSb−(conf_win_left_offset<<Prec) is calculated                     and used to derive the position of the reference                     sample, wherein xSb represents the horizontal                     position of the current sample in the current                     picture. conf_win_left_offset represents the                     horizontal position of the top-left sample in the                     conformance window of the current picture. Prec                     presents the precision of xSb and xSb′ wherein                     (xSb>>Prec) may show the actual horizontal                     coordinate of current sample relative to the current                     picture. For example, Prec=0 or Prec=4.             -   ii. In one example, horizontal position (denoted as Rx′)                 of the reference sample relative to the top-left                 position of the conformance window in the reference                 picture is calculated.                 -   1) The calculation of Rx′ may depend on xSb′, and/or                     a motion vector, and/or a resampling ratio.             -   iii. In one example, horizontal position (denoted as Rx)                 of the reference sample relative in the reference                 picture is calculated depending on Rx′.                 -   1) For example,                     Rx=Rx′+(conf_win_left_offset_ref<<Prec) is                     calculated, wherein conf_win_left_offset_ref                     represents the horizontal position of the top-left                     sample in the conformance window of the reference                     picture. Prec presents the precision of Rx and Rx′.                     For example, Prec=0 or Prec=4.             -   iv. In one example, Rx may be calculated directly                 depending on xSb′, and/or a motion vector, and/or a                 resampling ratio. In other words, the two steps of                 derivation on Rx′ and Rx are combined into a one-step                 calculation.             -   v. Whether to and/or how to use the left position (e.g.                 conf_win_left_offset as defined in VVC) of the                 conformance window of the current picture and/or the                 reference picture may depend on the color components                 and/or color formats.                 -   1) For example, conf_win_left_offset may be revised                     as                     conf_win_left_offset=conf_win_left_offset*SubWidthC,                     wherein SubWidthC defines the horizontal sampling                     step of a color component. E.g., SubWidthC is equal                     to 1 for the luma component. SubWidthC is equal to 2                     for a chroma component when the color format is                     4:2:0 or 4:2:2.                 -   2) For example, conf_win_left_offset may be revised                     as                     conf_win_left_offset=conf_win_left_offset/SubWidthC,                     wherein SubWidthC defines the horizontal sampling                     step of a color component. E.g., SubWidthC is equal                     to 1 for the luma component. SubWidthC is equal to 2                     for a chroma component when the color format is                     4:2:0 or 4:2:2.         -   c. In one example, the derivation of the vertical position             (e.g. refy_(L) as defined in VVC) of a reference sample may             depend on the top position (e.g. conf_win_top_offset as             defined in VVC) of the conformance window of the current             picture and/or the reference picture.             -   i. In one example, the vertical position (denoted as                 ySb′) of the current sample relative to the top-left                 position of the conformance window in the current                 picture is calculated and used to derive the position of                 the reference sample.                 -   1) For example, ySb′=ySb−(conf_win_top_offset<<Prec)                     is calculated and used to derive the position of the                     reference sample, wherein ySb represents the                     vertical position of the current sample in the                     current picture. conf_win_top_offset represents the                     vertical position of the top-left sample in the                     conformance window of the current picture. Prec                     presents the precision of ySb and ySb′. For example,                     Prec=0 or Prec=4.             -   ii. In one example, the vertical position (denoted as                 Ry′) of the reference sample relative to the top-left                 position of the conformance window in the reference                 picture is calculated.                 -   1) The calculation of Ry′ may depend on ySb′, and/or                     a motion vector, and/or a resampling ratio.             -   iii. In one example, the vertical position (denoted as                 Ry) of the reference sample relative in the reference                 picture is calculated depending on Ry′.                 -   1) For example,                     Ry=Ry′+(conf_win_top_offset_ref<<Prec) is                     calculated, wherein conf_win_top_offset_ref                     represents the vertical position of the top-left                     sample in the conformance window of the reference                     picture. Prec presents the precision of Ry and Ry′.                     For example, Prec=0 or Prec=4.             -   iv. In one example, Ry may be calculated directly                 depending on ySb′, and/or a motion vector, and/or a                 resampling ratio. In other words, the two steps of                 derivation on Ry′ and Ry are combined into a one-step                 calculation.             -   v. Whether to and/or how to use the top position (e.g.                 conf_win_top_offset as defined in VVC) of the                 conformance window of the current picture and/or the                 reference picture may depend on the color components                 and/or color formats.                 -   1) For example, conf_win_top_offset may be revised                     as                     conf_win_top_offset=conf_win_top_offset*SubHeightC,                     wherein SubHeightC defines the vertical sampling                     step of a color component. E.g., SubHeightC is equal                     to 1 for the luma component. SubHeightC is equal to                     2 for a chroma component when the color format is                     4:2:0.                 -   2) For example, conf_win_top_offset may be revised                     as                     conf_win_top_offset=conf_win_top_offset/SubHeightC,                     wherein SubHeightC defines the vertical sampling                     step of a color component. E.g., SubHeightC is equal                     to 1 for the luma component. SubHeightC is equal to                     2 for a chroma component when the color format is                     4:2:0.     -   28. It is proposed that the integer part of the horizontal         coordinate of a reference sample may be clipped to [minW, maxW].         Suppose the width and height of the conformance window of the         reference picture are denoted as W and H, respectively. The         width and height of the conformance window of a reference         picture are denoted as W′ and H′. The top-left position of the         conformance window in the reference picture are denoted as (X0,         Y0).         -   a. In one example, minW is equal to 0.         -   b. In one example, minW is equal to X0.         -   c. In one example, maxW is equal to W−1.         -   d. In one example, maxW is equal to W′−1.         -   e. In one example, maxW is equal to X0+W′−1.         -   f. In one example, minW and/or maxW may be modified based on             color format and/or color component.             -   i. For example, minW is modified to be minW*SubC.             -   ii. For example, minW is modified to be minW/SubC.             -   iii. For example, maxW is modified to be maxW*SubC.             -   iv. For example, maxW is modified to be maxW/SubC.             -   v. In one example, SubC is equal to 1 for the luma                 component.             -   vi. In one example, SubC is equal to 2 for a chroma                 component when the color format is 4:2:0.             -   vii. In one example, SubC is equal to 2 for a chroma                 component when the color format is 4:2:2.             -   viii. In one example, SubC is equal to 1 for a chroma                 component when the color format is 4:4:4.         -   g. In one example, the whether to and/or how to do the             clipping may depend on the dimensions of the current picture             (or the conformance window in it) and the dimensions of the             reference picture (or the conformance window in it).             -   i. In one example, the clipping is done only when the                 dimensions of the current picture (or the conformance                 window in it) and the dimensions of the reference                 picture (or the conformance window in it) are different.     -   29. It is proposed that the integer part of the vertical         coordinate of a reference sample may be clipped to [minH, maxH].         Suppose the width and height of the conformance window of the         reference picture are denoted as W and H, respectively. The         width and height of the conformance window of a reference         picture are denoted as W′ and H′. The top-left position of the         conformance window in the reference picture are denoted as (X0,         Y0).         -   a. In one example, minH is equal to 0.         -   b. In one example, minH is equal to Y0.         -   c. In one example, maxH is equal to H−1.         -   d. In one example, maxH is equal to H′−1.         -   e. In one example, maxH is equal to Y0+H′−1.         -   f. In one example, minH and/or maxH may be modified based on             color format and/or color component.             -   i. For example, minH is modified to be minH*SubC.             -   ii. For example, minH is modified to be minH/SubC.             -   iii. For example, maxH is modified to be maxH*SubC.             -   iv. For example, maxH is modified to be maxH/SubC.             -   v. In one example, SubC is equal to 1 for the luma                 component.             -   vi. In one example, SubC is equal to 2 for a chroma                 component when the color format is 4:2:0.             -   vii. In one example, SubC is equal to 1 for a chroma                 component when the color format is 4:2:2.             -   viii. In one example, SubC is equal to 1 for a chroma                 component when the color format is 4:4:4.         -   g. In one example, the whether to and/or how to do the             clipping may depend on the dimensions of the current picture             (or the conformance window in it) and the dimensions of the             reference picture (or the conformance window in it).             -   i. In one example, the clipping is done only when the                 dimensions of the current picture (or the conformance                 window in it) and the dimensions of the reference                 picture (or the conformance window in it) are different.

In the following discussion, a first syntax element is asserted to be “corresponding” to a second syntax element, if the two syntax elements have an equivalent functionality but may be signaled at different video unit (e.g. VPS/SPS/PPS/slice header/picture header etc.)

-   -   30. It is proposed that a syntax element may be signaled in a         first video unit (e.g. picture header or PPS) and no         corresponding syntax element is signaled in a second video unit         at a higher level (such as SPS) or a lower level (such as slice         header).         -   a. Alternatively, a first syntax element may be signaled in             the first video unit (e.g. picture header or PPS) and a             corresponding second syntax element may be signaled in a             second video unit at a lower level (such as slice header).             -   i. Alternatively, an indicator may be signaled in the                 second video unit to inform whether the second syntax                 element is signaled thereafter.             -   ii. In one example, the slice associated with the second                 video unit (such as slice header) may follow the                 indication of the second syntax element instead of the                 first one if the second one is signaled.             -   iii. An indicator associated with the first syntax                 element may be signaled in the first video unit to                 inform whether the second syntax element is signaled in                 any slice (or other video unit) associated with the                 first video unit.         -   b. Alternatively, a first syntax element may be signaled in             a first video unit at a higher level (such as VPS/SPS/PPS),             and a corresponding second syntax element may be signaled in             the second video unit (such as picture header).             -   i. Alternatively, an indicator may be signaled to inform                 whether the second syntax element is signaled                 thereafter.             -   ii. In one example, the picture (which may be                 partitioned into slices) associated with the second                 video unit may follow the indication of the second                 syntax element instead of the first one if the second                 one is signaled.         -   c. A first syntax element in the picture header may have an             equivalent functionality as a second syntax element in the             slice header as specified in section 2.6 (such as but             limited to slice_temporal_mvp_enabled_flag, cabac_init_flag,             six_minus_max_num_merge_cand,             five_minus_max_num_subblock_merge_cand,             slice_fpel_mmvd_enabled_flag, slice_disable_bdof_dmvr_flag,             max_num_merge_cand_minus_max_num_triangle_cand,             slice_fpel_mmvd_enabled_flag,             slice_six_minus_max_num_ibc_merge_cand,             slice_joint_cbcr_sign_flag, slice_qp_delta, . . . ) but             control all slices of the picture.         -   d. A first syntax element in SPS as specified in section 2.6             may have an equivalent functionality as a second syntax             element in the picture header (such as but limited to             sps_bdof_dmvr_slice_present_flag, sps_mmvd_enabled_flag,             sps_isp_enabled_flag, sps_mrl_enabled_flag,             sps_mip_enabled_flag, sps_cclm_enabled_flag,             sps_mts_enabled_flag . . . ) but control only the associated             picture (which may be partitioned into slices).         -   e. A first syntax element in PPS as specified in section 2.7             may have an equivalent functionality as a second syntax             element in the picture header (such as but limited to             entropy_coding_sync_enabled_flag,             entry_point_offsets_present_flag, cabac_init_present_flag,             rpl1_idx_present_flag . . . ) but control only the             associated picture (which may be partitioned into slices).     -   31. Syntax elements signaled in the picture header are decoupled         from other syntax elements signaled or derived in the         SPS/VPS/DPS.     -   32. Indications of enabling/disabling of DMVR and BDOF may be         signaled separately in picture header, instead of being         controlled by the same flag (e.g, pic_disable_bdof_dmvr_flag).     -   33. Indications of enabling/disabling of PROF/cross-component         ALF/inter prediction with geometric partitioning (GEO) may be         signaled in picture headers.         -   a. Alternatively, the indication of enabling/disabling PROF             in picture header may be conditionally signaled according to             the PROF enabling flag in SPS.         -   b. Alternatively, the indication of enabling/disabling             cross-component ALF (CCALF) in picture header may be             conditionally signaled according to the CCALF enabling flag             in SPS.         -   c. Alternatively, the indication of enabling/disabling GEO             in picture header may be conditionally signaled according to             the GEO enabling flag in SPS.         -   d. Alternatively, furthermore, indications of             enabling/disabling of PROF/cross-component ALF/inter             prediction with geometric partitioning (GEO) in slice             headers may be conditionally signaled according to those             syntax elements signaled in picture header instead of SPS.     -   34. Indications of prediction types of slices/bricks/tiles (or         other video units smaller than a picture) in the same picture         may be signaled in picture header.         -   a. In one example, an indication of whether all             slices/bricks/tiles (or other video units smaller than a             picture) are all intra-coded (e.g., all I slices) may be             signaled in the picture header.             -   i. Alternatively, furthermore, the slice types may not                 be signaled in slice header if the indication tells all                 slices within the picture are I slices.         -   b. Alternatively, an indication of whether at least one of             slices/bricks/tiles (or other video units smaller than a             picture) is not intra-coded (e.g., at least one non-I             slices) may be signaled in the picture header.         -   c. Alternatively, an indication of whether all             slices/bricks/tiles (or other video units smaller than a             picture) are all with the same prediction types (e.g., I/P/B             slices) may be signaled in the picture header.             -   i. Alternatively, furthermore, the slice types may not                 be signaled in slice header.             -   ii. Alternatively, furthermore, indication of tools                 which are allowed for specific prediction types (e.g,                 DMVR/BDOF/TPM/GEO are only allowed for B slices; dual                 tree is only allowed for I slices) may be conditionally                 signaled according to the indication of prediction                 types.         -   d. Alternatively, furthermore, signaling of indications of             enabling/disabling tools may depend on the indications of             prediction types mentioned in above sub-bullets.             -   i. Alternatively, furthermore, indications of                 enabling/disabling tools may be derived according to the                 indications of prediction types mentioned in above                 sub-bullets.     -   35. In this disclosure (bullet 1-bullet 29), the term         “conformance window” may be replaced by other terms such as         “scaling window”. A scaling window may be signaled differently         to the conformance window and is used to derive the scaling         ratio and/or top-left offset used to derive the reference sample         position for RPR.         -   a. In one example, the scaling window may be constrained by             the conformance window. For example, in a conformance             bit-stream, the scaling window must be contained by the             conformance window.     -   36. Whether and/or how to signal the allowed max block size for         transform-skip-coded blocks may depend on the max block size for         transform-coded blocks.         -   a. Alternatively, the max block size for             transform-skip-coded blocks cannot be larger than max block             size for transform-coded blocks in a conformance bitstream.     -   37. Whether and how to signal the indication of enabling Joint         Cb-Cr Residue (JCCR) coding (such as         sps_joint_cbcr_enabled_flag) may depend the color format (such         as 4:0:0, 4:2:0 etc.)         -   a. For example, the indication of enabling Joint Cb-Cr             Residue (JCCR) may not be signaled if the color format is             4:0:0. An exemplary syntax design is as below:

 sps_joint_cbcr_enabled_flag u(1) Downsampling Filter Type for Chroma Blending Mask Generation in TPM/GEO

-   -   38. The type of downsampling filter used for blending weights         derivation for chroma samples may be signalled at video unit         level (such as SPS/VPS/PPS/Picture header/Subpicture/Slice/Slice         header/Tile/Brick/CTU/VPDU level).         -   a. In one example, a high level flag may be signaled to             switch between different chroma format types of content.             -   i. In one example, a high level flag may be signaled to                 switch between chroma format type 0 and chroma format                 type 2.             -   ii. In one example, a flag may be signaled for                 specifying whether the top-left downsampled luma weights                 in TPM/GEO prediction mode is collocated with the                 top-left luma weights (e.g., chroma sample location type                 0).             -   iii. In one example, a flag may be signaled for                 specifying whether the top-left downsampled luma sample                 in TPM/GEO prediction mode is horizontally co-sited with                 the top-left luma sample but vertically shifted by 0.5                 units of luma samples relatively to the top-left luma                 sample (e.g., chroma sample location type 2).         -   b. In one example, the type of downsampling filter may be             signaled for 4:2:0 chroma format and/or 4:2:2 chroma format.         -   c. In one example, a flag may be signaled for specifying the             type of chroma downsampling filter used for TPM/GEO             prediction.             -   i. In one example, the flag may be signaled for whether                 to use downsampling filter A or downsampling filter B                 for the chroma weights derivation in TPM/GEO prediction                 mode.     -   39. The type of downsampling filter used for blending weights         derivation for chroma samples may be derived at video unit level         (such as SPS/VPS/PPS/Picture header/Subpicture/Slice/Slice         header/Tile/Brick/CTU/VPDU level).         -   a. In one example, a lookup table may be defined to specify             the correspondence relationship between the chroma             subsampling filter type and the chroma format types of             content.     -   40. A specified downsampling filter may be used for TPM/GEO         prediction mode in case of different chroma sample location         type.         -   a. In one example, chroma weights of TPM/GEO may be             subsampled from the collocated top-left luma weights in case             of a certain chroma sample location type (e.g., chroma             sample location type 0).         -   b. In one example, in case of a certain chroma sample             location type (e.g., chroma sample location type 0 or 2), a             specified X-tap filter (X is a constant such as X=6 or 5)             may be used for chroma weights subsampling in TPM/GEO             prediction mode.     -   41. In a video unit (e.g. SPS, PPS, picture header, slice header         etc.), a first syntax element (such as a flag) may be signaled         to indicate whether Multiple Transform Selection (MTS) is         disabled for all blocks (slices/pictures).         -   a. A second syntax element indicating how to apply MTS (such             as enable MTS/disable MTS/implicit MTS/explicit MTS) on             intra-coding blocks (slices/pictures) is signaled             conditionally on the first syntax element. For example, the             second syntax element is signaled only when the first syntax             element indicates that MTS is not disabled for all blocks             (slices/pictures).         -   b. A third syntax element indicating how to apply MTS (such             as enable MTS/disable MTS/implicit MTS/explicit MTS) on             inter-coding blocks (slices/pictures) is signaled             conditionally on the first syntax element. For example, the             third syntax element is signaled only when the first syntax             element indicates that MTS is not disabled for all blocks             (slices/pictures).         -   c. An exemplary syntax design is as below

...  enable_mts_flag  if( enable_mts_flag){   mts_control_intra   mts_control_inter } ...

-   -   -   d. The third syntax element may be signaled conditionally on             whether Sub-Block Transform (SBT) is applied or not. An             exemplary syntax design is as below

...  if (sps_sbt_enabled_flag)   mts_control_inter ...

-   -   -   e. An exemplary syntax design is as below

-

-

Determination of Usage of a Coding Tool X

-   -   42. The determination of whether to and/or how to enable a         coding tool X may depend on the width and/height of a         considering picture of one or multiple reference pictures and/or         current picture.         -   a. The width and/height of a considering picture of one or             multiple reference pictures and/or current picture may be             modified to make the determination.         -   b. The considering picture may be defined by the conformance             window or the scaling window.             -   i. The considering picture may be the whole picture.         -   c. In one example, whether to and/or how to enable a coding             tool X may depend on the width of a picture minus one or             multiple offsets in the horizontal and/or height of a             picture minus an offset in the vertical direction.             -   i. In one example, the horizontal offset may be defined                 as the scaling_win_left_offset.             -   ii. In one example, the vertical offset may be defined                 as the scaling_win_top_offset.             -   iii. In one example, the horizontal offset may be                 defined as                 (scaling_win_right_offset+scaling_win_left_offset).             -   iv. In one example, the vertical offset may be defined                 as (scaling_win_bottom_offset+scaling_win_top_offset).             -   v. In one example, the horizontal offset may be defined                 as                 SubWidthC*(scaling_win_right_offset+scaling_win_left_offset).             -   vi. In one example, the vertical offset may be defined                 as                 SubHeightC*(scaling_win_bottom_offset+scaling_win_top_offset).         -   d. In one example, if at least one of the two considering             reference pictures have different resolution (either width             or height) with current picture, the coding tool X is             disabled.             -   i. Alternatively, if at least one of the two output                 reference pictures have a dimension (either width or                 height) larger than that of the current picture, the                 coding tool X is disabled.         -   e. In one example, if one considering reference picture for             a reference picture list L has different resolution with             current picture, the coding tool X is disabled for the             reference picture list L.             -   i. Alternatively, if one considering reference picture                 for a reference picture list L has a dimension (either                 width or height) larger than that of the current                 picture, the coding tool X is disabled for the reference                 picture list L.         -   f. In one example, if two considering reference pictures of             two reference picture lists are with different resolutions,             the coding tool may be disabled.             -   i. Alternatively, the indications of the coding tool may                 be conditionally signalled according to resolutions.             -   ii. Alternatively, signalling of the indications of the                 coding tool may be skipped.         -   g. In one example, if two considering reference pictures of             two merge candidates utilized to derive a first pairwise             merge candidate for at least one reference picture list, the             coding tool may be disabled, e.g., the first pairwise merge             candidate is marked as unavailable.             -   i. Alternatively, if two considering reference pictures                 of two merge candidates utilized to derive a first                 pairwise merge candidate for both reference picture                 lists, the coding tool may be disabled, e.g., the first                 pairwise merge candidate is marked as unavailable.         -   h. In one example, the decoding process of the coding tool             may be modified with the consideration of picture dimension.             -   i. In one example, the derivation of MD for another                 reference picture list (e.g, list 1) in SMVD may be                 based on the resolution differences (e.g., scaling                 factors) of at least one of the two target SMVD                 reference pictures.             -   ii. In one example, the derivation of pairwise merge                 candidate may be based on the resolution differences                 (e.g., scaling factors) of at least one of the two                 reference pictures associated with two reference                 pictures, e.g., linear weighted average may be applied                 instead of equal weights.         -   i. In one example, X may be:             -   i. DMVR/BDOF/PROF/SMVD/MMVD/other coding tools that                 refine motion/prediction at the decoder side             -   ii. TMVP/other coding tools rely on temporal motion                 information             -   iii. MTS or other transform coding tools             -   iv. CC-ALF             -   v. TPM             -   vi. GEO             -   vii. Switchable interpolation filter (e.g., alternative                 interpolation filter for half-pel motion compensation)             -   viii. The blending process in TPM/GEO/other coding tools                 that split one block into multiple partitions.             -   ix. A coding tool that replies on the stored information                 in a picture different from current picture             -   x. Pairwise merge candidate (when certain conditions                 related to resolution are not satisfied, pairwise merge                 candidate is not generated)             -   xi. Bi-prediction with CU-level Weights (BCW).             -   xii. Weighted prediction.             -   xiii. Affine prediction             -   xiv. Adaptive Motion Vector Resolution (AMVR)     -   43. Whether to and/or how to signal the usage of a coding tool         may depend on the width and/height of an considering picture of         one or multiple reference pictures and/or current picture.         -   a. The width and/height of a considering picture of one or             multiple reference pictures and/or current picture may be             modified to make the determination.         -   b. The considering picture may be defined by the conformance             window or the scaling window as defined in JVET-P0590.             -   xv. The considering picture may be the whole picture.         -   c. In one example, X may be the adaptive motion vector             resolution (AMVR).         -   d. In one example, X may be the merge with MV differences             (MMVD) method.             -   xvi. In one example, the construction of symmetric                 motion vector difference reference indices may depend on                 the picture resolutions/indications of RPR cases for                 different reference pictures.         -   e. In one example, X may be the symmetric MVD (SMVD) method.         -   f. In one example, X may be the QT/BT/TT or other             partitioning types.         -   g. In one example, X may be Bi-prediction with CU-level             Weights (BCW).         -   h. In one example, X may be Weighted prediction.         -   i. In one example, X may be Affine prediction.         -   j. In one example, whether to signal the indication of usage             of half-pel motion vector precision/switchable interpolation             filter may depend on the resolution information/whether RPR             is enabled for current block.         -   k. In one example, the signalling of amvr_precision_idx may             depend on the resolution information/whether RPR is enabled             for current block.         -   l. In one example, the signalling of             sym_mvd_flag/mmvd_merge_flag may depend on the resolution             information/whether RPR is enabled for current block.         -   m. A conformance bitstream shall satisfy that the ½-pel MV             and/or MVD precision (e.g, the alternative interpolation             filter/switchable interpolation filter) is disallowed when             the width and/height of a considering picture of one or             multiple reference pictures is different from that of             current output picture.     -   44. It is proposed that AMVR with ½-pel MV and/or MVD precision         (or alternative interpolation filter/switchable interpolation         filter) may be still enabled for a block in RPR.         -   a. Alternatively, furthermore, a different interpolation             filter may be applied for blocks with ½-pel or other             precisions.     -   45. The condition check of same/different resolutions in above         bullets may be replaced by adding a flag for a reference picture         and checking the flags associated with reference pictures.         -   a. In one example, the process of setting the flag to be             true or false (e.g., to indicate whether the reference             picture is RPR case or non-RPR case) may be invoked during             the reference picture list construction process.             -   xvii. For example, the following may be applied:                 -   fRefWidth is set equal to PicOutputWidthL of the                     reference picture RefPicList[i][j] in luma samples,                     where PicOutputWidthL represents the width of the                     considering picture of the reference picture.                 -   fRefWidth is set equal to PicOutputHeightL of the                     reference picture RefPicList[i][j] in luma samples,                     where PicOutputHeightL represents the height of the                     considering picture of the reference picture.                     RefPicScale[i][j][0]((fRefWidth<<14)+(PicOutputWidthL>>1))/PicOutputWidthL,                 -   where                 -   PicOutputWidthL represents the width of the                     considering picture of the current picture.                     RefPicScale[i][j][1]((fRefHeight<<14)+(PicOutputHeightL>>1))/PicOutputHeightL,                 -   where PicOutputWidthL represents the height of the                     considering picture of the current picture                     RefPicIsScaled[i][j]=(RefPicScale[i][j][0]!=(1<<14))∥(RefPicScale[i][j][1]!=(1<14))                 -   wherein RefPicList[i][j] represents the j-th                     reference picture in reference picture list i.         -   b. In one example, when either RefPicIsScaled[0][refIdxL0]             is unequal to 0 or RefPicIsScaled[1][refIdxL1] is unequal to             0, a coding tool X (e.g.,             DMVR/BDOF/SMVD/MMVD/SMVD/PROF/those mentioned in above             bullets) may be disabled.         -   c. In one example, when both RefPicIsScaled[0][refIdxL0] and             RefPicIsScaled[1][refIdxL1] are unequal to 0, a coding tool             X (e.g., DMVR/BDOF/SMVD/MMVD/SMVD/PROF/those mentioned in             above bullets) may be disabled.         -   d. In one example, when RefPicIsScaled[0][refIdxL0] is             unequal to 0, a coding tool X (e.g., PROF or those mentioned             in above bullets) may be disabled for reference picture list             0.         -   e. In one example, when RefPicIsScaled[1][refIdxL1] is             unequal to 0, a coding tool X (e.g., PROF or those mentioned             in above bullets) may be disabled for reference picture list             1.     -   46. The SAD and/or threshold used by BDOF/DMVR may be dependent         on the bit-depth.         -   f. In one example, the calculated SAD value may be firstly             shifted by a function of bit-depth before being utilized to             be compared to a threshold.         -   g. In one example, the calculated SAD value may be directly             compared with a modified threshold which may depend on a             function of bit-depth.

5. Additional Embodiments

In the following, text changes are shown in underlined bold italicized font.

5.1. Embodiment of Constrains on the Conformance Window

conf_win_left_offset, conf_win_right_offset, conf_win_top_offset, and conf_win_bottom_offset specify the samples of the pictures in the CVS that are output from the decoding process, in terms of a rectangular region specified in picture coordinates for output. When conformance_window_flag is equal to 0, the values of conf_win_left_offset, conf_win_right_offset, conf_win_top_offset, and conf_win_bottom_offset are inferred to be equal to 0.

The conformance cropping window contains the luma samples with horizontal picture coordinates from SubWidthC*conf_win_left_offset to pic_width_in_luma_samples−(SubWidthC*conf_win_right_offset+1) and vertical picture coordinates from SubHeightC*conf_win_top_offset to pic_height_in_luma_samples−(SubHeightC*conf_win_bottom_offset+1), inclusive.

The value of SubWidthC*(conf_win_left_offset+conf_win_right_offset) shall be less than pic_width_in_luma_samples, and the value of SubHeightC*(conf_win_top_offset+conf_win_bottom_offset) shall be less than pic_height_in_luma_samples.

The variables PicOutputWidthL and PicOutputHeightL are derived as follows: PicOutputWidthL=pic_width_in_luma_samples−SubWidthC*(conf_win_right_offset+conf_win_left_offset)  (7-43) PicOutputHeightL=pic_height_in_pic_size_units−SubHeightC*(conf_win_bottom_offset+conf_win_top_offset)  (7-44)

When ChromaArrayType is not equal to 0, the corresponding specified samples of the two chroma arrays are the samples having picture coordinates (x/SubWidthC, y/SubHeightC), where (x, y) are the picture coordinates of the specified luma samples.

-   -   

    -   

    -   

    -   

5.2. Embodiment 1 of Reference Sample Position Derivation

8.5.6.3.1 General

. . .

The variable fRefWidth is set equal to the PicOutputWidthL of the reference picture in luma samples.

The variable fRefHeight is set equal to PicOutputHeightL of the reference picture in luma samples.

The motion vector mvLX is set equal to (refMvLX−mvOffset).

-   -   If cIdx is equal to 0, the following applies:         -   The scaling factors and their fixed-point representations             are defined as             hori_scale_fp=((fRefWidth<<14)+(PicOutputWidthL>>1))/PicOutputWidthL  (8-753)             vert_scale_fp=((fRefHeight<<14)+(PicOutputHeightL>>1))/PicOutputHeightL  (8-754)         -   Let (xIntL, yIntL) be a luma location given in full-sample             units and (xFracL, yFracL) be an offset given in 1/16-sample             units. These variables are used only in this clause for             specifying fractional-sample locations inside the reference             sample arrays refPicLX.         -   The top-left coordinate of the bounding block for reference             sample padding (xSbInt_(L), ySbInt_(L)) is set equal to             (xSb+(mvLX[0]>>4), ySb+(mvLX[1]>>4)).         -   For each luma sample location (x_(L)=0 . . .             sbWidth−1+brdExtSize, y_(L)=0 . . . sbHeight−1+brdExtSize)             inside the prediction luma sample array predSamplesLX, the             corresponding prediction luma sample value             predSamplesLX[x_(L)][y_(L)] is derived as follows:             -   Let (refxSb_(L), refySb_(L)) and (refx_(L), refy_(L)) be                 luma locations pointed to by a motion vector                 (refMvLX[0], refMvLX[1]) given in 1/16-sample units. The                 variables refxSb_(L), refx_(L), refySb_(L), and refy_(L)                 are derived as follows:                 refxSb_(L)=((                 <<4)+refMvLX[0])*hori_scale_fp  (8-755)                 refx _(L)=((Sign(refxSb)*((Abs(refxSb)+128)>>8)+x                 _(L)*((hori_scale_fp+8)>>4))+32)>>6  (8-756)                 refySb_(L)=((                 <<4)+refMvLX[1])*vert_scale_fp  (8-757)                 refy _(L)=((Sign(refySb)*((Abs(refySb)+128)>>8)+y                 _(L)*((vert_scale_fp+8)>>4))+32)>>6  (8-758)             -   The variables xInt_(L), yInt_(L), xFrac_(L) and                 yFrac_(L) are derived as follows:                 xInt_(L)=refx _(L)>>4  (8-759)                 yInt_(L)=refy _(L)>>4  (8-760)                 xFrac_(L)=refx _(L)&15  (8-761)                 yFrac_(L)=refy _(L)&15  (8-762)         -   If bdofFlag is equal to TRUE or             (sps_affine_prof_enabled_flag is equal to TRUE and             inter_affine_flag[xSb][ySb] is equal to TRUE), and one or             more of the following conditions are true, the prediction             luma sample value predSamplesLX[x_(L)][y_(L)] is derived by             invoking the luma integer sample fetching process as             specified in clause 8.5.6.3.3 with             (xInt_(L)+(xFrac_(L)>>3)−1), yInt_(L)+(yFrac_(L)>>3)−1) and             refPicLX as inputs.             -   x_(L) is equal to 0.             -   x_(L) is equal to sbWidth+1.             -   y_(L) is equal to 0.             -   y_(L) is equal to sbHeight+1.             -   Otherwise, the prediction luma sample value                 predSamplesLX[xL][yL] is derived by invoking the luma                 sample 8-tap interpolation filtering process as                 specified in clause 8.5.6.3.2 with                 (xIntL−(brdExtSize>0?1:0), yIntL−(brdExtSize>0?1:0)),                 (xFracL, yFracL), (xSbInt_(L), ySbInt_(L)), refPicLX,                 hpelIfIdx, sbWidth, sbHeight and (xSb, ySb) as inputs.     -   Otherwise (cIdx is not equal to 0), the following applies:         -   Let (xIntC, yIntC) be a chroma location given in full-sample             units and (xFrac_(C), yFrac_(C)) be an offset given in 1/32             sample units. These variables are used only in this clause             for specifying general fractional-sample locations inside             the reference sample arrays refPicLX.         -   The top-left coordinate of the bounding block for reference             sample padding (xSbIntC, ySbIntC) is set equal to             ((xSb/SubWidthC)+(mvLX[0]>>5),             (ySb/SubHeightC)+(mvLX[1]>>5)).         -   For each chroma sample location (xC=0 . . . sbWidth−1, yC=0             . . . sbHeight−1) inside the prediction chroma sample arrays             predSamplesLX, the corresponding prediction chroma sample             value predSamplesLX[xC][yC] is derived as follows:             -   Let (refxSb_(C), refySb_(C)) and (refx_(C), refy_(C)) be                 chroma locations pointed to by a motion vector (mvLX[0],                 mvLX[1]) given in 1/32-sample units. The variables                 refxSb_(C), refySb_(C), refx_(C) and refy_(C) are                 derived as follows:                 refxSb_(C)=((                 /SubWidthC<<5)+mvLX[0])*hori_scale_fp   (8-763)                 refx                 _(C)=((Sign(refxSb_(C))*((Abs(refxSb_(C))+256)>>9)+xC*((hori_scale_fp+8)>>4))+16)>>5  (8-764)                 refySb_(C)=((                 /SubHeightC<<5)+mvLX[1])*vert_scale_fp   (8-765)                 refy                 _(C)=((Sign(refySb_(C))*((Abs(refySb_(C))+256)>>9)+yC*((vert_scale_fp+8)>>4))+16)>>5  (8-766)             -   The variables xInt_(C), yInt_(C), xFrac_(C) and                 yFrac_(C) are derived as follows:                 xInt_(C)=refx _(C)>>5  (8-767)                 yInt_(C)=refy _(C)>>5  (8-768)                 xFrac_(C)=refy _(C)&31  (8-769)                 yFrac_(C)=refy _(C)&31  (8-770)

5.3. Embodiment 2 of Reference Sample Position Derivation

8.5.6.3.1 General

. . .

The variable fRefWidth is set equal to the PicOutputWidthL of the reference picture in luma samples.

The variable fRefHeight is set equal to the PicOutputHeightL of the reference picture in luma samples.

The motion vectormvLX is set equal to (refMvLX−mvOffset).

-   -   If cIdx is equal to 0, the following applies:         -   The scaling factors and their fixed-point representations             are defined as             hori_scale_fp=((fRefWidth<<14)+(PicOutputWidthL>>1))/PicOutputWidthL  (8-753)             vert_scale_fp=((fRefHeight<<14)+(PicOutputHeightL>>1))/PicOutputHeightL  (8-754)         -   Let (xIntL, yIntL) be a luma location given in full-sample             units and (xFracL, yFracL) be an offset given in 1/16-sample             units. These variables are used only in this clause for             specifying fractional-sample locations inside the reference             sample arrays refPicLX.         -   The top-left coordinate of the bounding block for reference             sample padding (xSbInt_(L), ySbInt_(L)) is set equal to             (xSb+(mvLX[0]>>4), ySb+(mvLX[1]>>4)).         -   For each luma sample location (x_(L)=0 . . .             sbWidth−1+brdExtSize, y_(L)=0 . . . sbHeight−1+brdExtSize)             inside the prediction luma sample array predSamplesLX, the             corresponding prediction luma sample value             predSamplesLX[x_(L)][y_(L)] is derived as follows:             -   Let (refxSb_(L), refySb_(L)) and (refx_(L), refy_(L)) be                 luma locations pointed to by a motion vector                 (refMvLX[0], refMvLX[1]) given in 1/16-sample units. The                 variables refxSb_(L), refx_(L), refySb_(L), and refy_(L)                 are derived as follows:                 refxSb_(L)=((                 <<4)+refMvLX[0])*hori_scale_fp  (8-755)                 refx _(L)=((Sign(refxSb)*((Abs(refxSb)+128)>>8)+x                 _(L)*((hori_scale_fp+8)>>4))                 +32)>>6  (8-756)                 refySb_(L)=((                 <<4)+refMvLX[1])*vert_scale_fp  (8-757)                 refy                 _(L)=((Sign(refySb)*((Abs(refySb)+128)>>8)+yL*((vert_scale_fp+8)>>4))                 +32)>>6  (8-758)             -   The variables xInt_(L), yInt_(L), xFrac_(L) and                 yFrac_(L) are derived as follows:                 xInt_(L)=refx _(L)>>4  (8-759)                 yInt_(L)=refy _(L)>>4  (8-760)                 xFrac_(L)=refx _(L)&15  (8-761)                 yFrac_(L)=refy _(L)&15  (8-762)         -   If bdofFlag is equal to TRUE or             (sps_affine_prof_enabled_flag is equal to TRUE and             inter_affine_flag[xSb][ySb] is equal to TRUE), and one or             more of the following conditions are true, the prediction             luma sample value predSamplesLX[x_(L)][y_(L)] is derived by             invoking the luma integer sample fetching process as             specified in clause 8.5.6.3.3 with             (xInt_(L)+(xFrac_(L)>>3)−1), yInt_(L)+(yFrac_(L)>>3)−1) and             refPicLX as inputs.             -   x_(L) is equal to 0.             -   x_(L) is equal to sbWidth+1.             -   y_(L) is equal to 0.             -   y_(L) is equal to sbHeight+1.         -   Otherwise, the prediction luma sample value             predSamplesLX[xL][yL] is derived by invoking the luma sample             8-tap interpolation filtering process as specified in clause             8.5.6.3.2 with (xIntL−(brdExtSize>0?1:0),             yIntL−(brdExtSize>0?1:0)), (xFracL, yFracL), (xSbInt_(L),             ySbInt_(L)), refPicLX, hpelIfIdx, sbWidth, sbHeight and             (xSb, ySb) as inputs.     -   Otherwise (cIdx is not equal to 0), the following applies:         -   Let (xIntC, yIntC) be a chroma location given in full-sample             units and (xFracC, yFracC) be an offset given in 1/32 sample             units. These variables are used only in this clause for             specifying general fractional-sample locations inside the             reference sample arrays refPicLX.         -   The top-left coordinate of the bounding block for reference             sample padding (xSbIntC, ySbIntC) is set equal to             ((xSb/SubWidthC)+(mvLX[0]>>5),             (ySb/SubHeightC)+(mvLX[1]>>5)).         -   For each chroma sample location (xC=0 . . . sbWidth−1, yC=0             . . . sbHeight−1) inside the prediction chroma sample arrays             predSamplesLX, the corresponding prediction chroma sample             value predSamplesLX[xC][yC] is derived as follows:             -   Let (refxSb_(C), refySb_(C)) and (refx_(C), refy_(C)) be                 chroma locations pointed to by a motion vector (mvLX[0],                 mvLX[1]) given in 1/32-sample units. The variables                 refxSb_(C), refySb_(C), refx_(C) and refy_(C) are                 derived as follows:                 refxSb_(C)=((                 /SubWidthC<<5)+mvLX[0])*hori_scale_fp   (8-763)                 refx                 _(C)=((Sign(refxSb_(C))*((Abs(refxSb_(C))+256)>>9)+xC*((hori_scale_fp+8)>>4))+16)>>5  (8-764)                 refySb_(C)=((                 /SubHeightC<<5)+mvLX[1])*vert_scale_fp   (8-765)                 refy                 _(C)=((Sign(refySb_(C))*((Abs(refySb_(C))+256)>>9)+yC*((vert_scale_fp+8)>>4))+16)>>5  (8-766)             -   The variables xInt_(C), yInt_(C), xFrac_(C) and                 yFrac_(C) are derived as follows:                 xInt_(C)=refx _(C)>>5  (8-767)                 yInt_(C)=refy _(C)>>5  (8-768)                 xFrac_(C)=refy _(C)&31  (8-769)                 yFrac_(C)=refy _(C)&31  (8-770)

5.4. Embodiment 3 of Reference Sample Position Derivation

8.5.6.3.1 General

. . .

The variable fRefWidth is set equal to the PicOutputWidthL of the reference picture in luma samples.

The variable fRefHeight is set equal to PicOutputHeightL of the reference picture in luma samples.

The motion vector mvLX is set equal to (refMvLX-mvOffset).

-   -   If cIdx is equal to 0, the following applies:         -   The scaling factors and their fixed-point representations             are defined as             hori_scale_fp=((fRefWidth<<14)+(PicOutputWidthL>>1))/PicOutputWidthL  (8-753)             vert_scale_fp=((fRefHeight<<14)+(PicOutputHeightL>>1))/PicOutputHeightL  (8-754)         -   Let (xIntL, yIntL) be a luma location given in full-sample             units and (xFracL, yFracL) be an offset given in 1/16-sample             units. These variables are used only in this clause for             specifying fractional-sample locations inside the reference             sample arrays refPicLX.         -   The top-left coordinate of the bounding block for reference             sample padding (xSbInt_(L), ySbInt_(L)) is set equal to             (xSb+(mvLX[0]>>4), ySb+(mvLX[1]>>4)).         -   For each luma sample location (x_(L)=0 . . .             sbWidth−1+brdExtSize, y_(L)=0 . . . sbHeight−1+brdExtSize)             inside the prediction luma sample array predSamplesLX, the             corresponding prediction luma sample value             predSamplesLX[x_(L)][y_(L)] is derived as follows:             -   Let (refxSb_(L), refySb_(L)) and (refx_(L), refy_(L)) be                 luma locations pointed to by a motion vector                 (refMvLX[0], refMvLX[1]) given in 1/16-sample units. The                 variables refxSb_(L), refx_(L), refySb_(L), and refy_(L)                 are derived as follows:                 refxSb_(L)=((                 <<4)+refMvLX[0])*hori_scale_fp  (8-755)                 refx _(L)=((Sign(refxSb)*((Abs(refxSb)+128)>>8)+x                 _(L)*((hori_scale_fp+8)>>4))                 +32)>>6  (8-756)                 refySb_(L)=((                 <<4)+refMvLX[1])*vert_scale_fp  (8-757)                 refy _(L)=((Sign(refySb)*((Abs(refySb)+128)>>8)+y                 _(L)*((vert_scale_fp+8)>>4))                 +32)>>6  (8-758)             -   The variables xInt_(L), yInt_(L), xFrac_(L) and                 yFrac_(L) are derived as follows:                 xInt_(L)=refx _(L)>>4  (8-759)                 yInt_(L)=refy _(L)>>4  (8-760)                 xFrac_(L)=refx _(L)&15  (8-761)                 yFrac_(L)=refy _(L)&15  (8-762)         -   If bdofFlag is equal to TRUE or             (sps_affine_prof_enabled_flag is equal to TRUE and             inter_affine_flag[xSb][ySb] is equal to TRUE), and one or             more of the following conditions are true, the prediction             luma sample value predSamplesLX[x_(L)][y_(L)] is derived by             invoking the luma integer sample fetching process as             specified in clause 8.5.6.3.3 with             (xInt_(L)+(xFrac_(L)>>3)−1), y Int_(L)+(yFrac_(L)>>3)−1) and             refPicLX as inputs.             -   x_(L) is equal to 0.             -   x_(L) is equal to sbWidth+1.             -   y_(L) is equal to 0.             -   y_(L) is equal to sbHeight+1.         -   Otherwise, the prediction luma sample value             predSamplesLX[xL][yL] is derived by invoking the luma sample             8-tap interpolation filtering process as specified in clause             8.5.6.3.2 with (xIntL−(brdExtSize>0?1:0),             yIntL−(brdExtSize>0?1:0)), (xFracL, yFracL), (xSbInt_(L),             ySbInt_(L)), refPicLX, hpelIfIdx, sbWidth, sbHeight and             (xSb, ySb) as inputs.     -   Otherwise (cIdx is not equal to 0), the following applies:         -   Let (xIntC, yIntC) be a chroma location given in full-sample             units and (xFracC, yFracC) be an offset given in 1/32 sample             units. These variables are used only in this clause for             specifying general fractional-sampi locations inside the             reference sample arrays refPicLX.         -   The top-left coordinate of the bounding block for reference             sample padding (xSbIntC, ySbIntC) is set equal to             ((xSb/SubWidthC)+(mvLX[0]>>5),             (ySb/SubHeightC)+(mvLX[1]>>5)).         -   For each chroma sample location (xC=0 . . . sbWidth−1, yC=0             . . . sbHeight−1) inside the prediction chroma sample arrays             predSamplesLX, the corresponding prediction chroma sample             value predSamplesLX[xC][yC] is derived as follows:             -   Let (refxSb_(C), refySb_(C)) and (refx_(C), refy_(C)) be                 chroma locations pointed to by a motion vector (mvLX[0],                 mvLX[1]) given in 1/32-sample units. The variables                 refxSb_(C), refySb_(C), refx_(C) and refy_(C) are                 derived as follows:                 refxSb_(C)=((                 /SubWidthC<<5)+mvLX[0])*hori_scale_fp  (8-763)                 refx                 _(C)=((Sign(refxSb_(C))*((Abs(refxSb_(C))+256)>>9)+xC*((hori_scale_fp+8)>>4))                 +16)>>5  (8-764)                 refySb_(C)=((                 /SubHeightC<<5)+mvLX[1])*vert_scale_fp  (8-765)                 refy                 _(C)=((Sign(refySb_(C))*((Abs(refySb_(C))+256)>>9)+yC*((vert_scale_fp+8)>>4))                 16)>>5  (8-766)             -   The variables xInt_(C), yInt_(C), xFrac_(C) and                 yFrac_(C) are derived as follows:                 xInt_(C)=refx _(C)>>5  (8-767)                 yInt_(C)=refy _(C)>>5  (8-768)                 xFrac_(C)=refy _(C)&31  (8-769)                 yFrac_(C)=refy _(C)&31  (8-770)

5.5. Embodiment 1 of reference sample position clipping

8.5.6.3.1 General

Inputs to this process are:

-   -   a luma location (xSb, ySb) specifying the top-left sample of the         current coding subblock relative to the top-left luma sample of         the current picture,     -   a variable sbWidth specifying the width of the current coding         subblock,     -   a variable sbHeight specifying the height of the current coding         subblock,     -   a motion vector offset mvOffset,     -   a refined motion vector refMvLX,     -   the selected reference picture sample array refPicLX,     -   the half sample interpolation filter index hpelIfIdx,     -   the bi-directional optical flow flag bdofFlag,     -   a variable cIdx specifying the colour component index of the         current block.

Outputs of this process are:

-   -   an (sbWidth+brdExtSize)×(sbHeight+brdExtSize) array         predSamplesLX of prediction sample values.

The prediction block border extension size brdExtSize is derived as follows: brdExtSize=(bdofFlag∥(inter_affine_flag[xSb][ySb]&&sps_affine_prof_enabled_flag))?2:0  (8-752)

The variable fRefWidth is set equal to the PicOutputWidthL of the reference picture in luma samples.

The variable fRefHeight is set equal to PicOutputHeightL of the reference picture in luma samples.

The motion vectormvLX is set equal to (refMvLX-mvOffset).

-   -   If cIdx is equal to 0, the following applies:         -   The scaling factors and their fixed-point representations             are defined as             hori_scale_fp=((fRefWidth<<14)+(PicOutputWidthL>>1))/PicOutputWidthL  (8-753)             vert_scale_fp=((fRefHeight<<14)+(PicOutputHeightL>>1))/PicOutputHeightL  (8-754)         -   Let (xIntL, yIntL) be a luma location given in full-sample             units and (xFracL, yFracL) be an offset given in 1/16-sample             units. These variables are used only in this clause for             specifying fractional-sample locations inside the reference             sample arrays refPicLX.         -   The top-left coordinate of the bounding block for reference             sample padding (xSbInt_(L), ySbInt_(L)) is set equal to             (xSb+(mvLX[0]>>4), ySb+(mvLX[1]>>4)).         -   For each luma sample location (x_(L)=0 . . .             sbWidth−1+brdExtSize, y_(L)=0 . . . sbHeight−1+brdExtSize)             inside the prediction luma sample array predSamplesLX, the             corresponding prediction luma sample value             predSamplesLX[x_(L)][y_(L)] is derived as follows:             -   Let (refxSb_(L), refySb_(L)) and (refx_(L), refy_(L)) be                 luma locations pointed to by a motion vector                 (refMvLX[0], refMvLX[1]) given in 1/16-sample units. The                 variables refxSb_(L), refx_(L), refySb_(L), and refy_(L)                 are derived as follows:                 refxSb_(L)=((xSb<<4)+refMvLX[0])*hori_scale_fp  (8-755)                 refx                 _(L)=((Sign(refxSb)*((Abs(refxSb)+128)>>8)+xL*((hori_scale_fp+8)>>4))+32)>>6  (8-756)                 refySb_(L)=((ySb<<4)+refMvLX[1])*vert_scale_fp  (8-757)                 refyL=((Sign(refySb)*((Abs(refySb)+128)>>8)+yL*((vert_scale_fp+8)>>4))+32)>>6  (8-758)             -   The variables xInt_(L), yInt_(L), xFrac_(L) and                 yFrac_(L) are derived as follows:                 xInt_(L)=                   (8-759)                 yInt_(L)=                   (8-760)                 xFrac_(L)=refx _(L)&15  (8-761)                 yFrac_(L)=refy _(L)&15  (8-762)         -   If bdofFlag is equal to TRUE or             (sps_affine_prof_enabled_flag is equal to TRUE and             inter_affine_flag[xSb][ySb] is equal to TRUE), and one or             more of the following conditions are true, the prediction             luma sample value predSamplesLX[x_(L)][y_(L)] is derived by             invoking the luma integer sample fetching process as             specified in clause 8.5.6.3.3 with             (xInt_(L)+(xFrac_(L)>>3)−1), yInt_(L)+(yFrac_(L)>>3)−1) and             refPicLX as inputs.             -   x_(L) is equal to 0.             -   XL is equal to sbWidth+1.             -   y_(L) is equal to 0.             -   y_(L) is equal to sbHeight+1.         -   Otherwise, the prediction luma sample value             predSamplesLX[xL][yL] is derived by invoking the luma sample             8-tap interpolation filtering process as specified in clause             8.5.6.3.2 with (xIntL−(brdExtSize>0?1:0),             yIntL−(brdExtSize>0?1:0)), (xFracL, yFracL), (xSbInt_(L),             ySbInt_(L)), refPicLX, hpelIfIdx, sbWidth, sbHeight and             (xSb, ySb) as inputs.     -   Otherwise (cIdx is not equal to 0), the following applies:         -   Let (xIntC, yIntC) be a chroma location given in full-sample             units and (xFracC, yFracC) be an offset given in 1/32 sample             units. These variables are used only in this clause for             specifying general fractional-sampb locations inside the             reference sample arrays refPicLX.         -   The top-left coordinate of the bounding block for reference             sample padding (xSbIntC, ySbIntC) is set equal to             ((xSb/SubWidthC)+(mvLX[0]>>5),             (ySb/SubHeightC)+(mvLX[1]>>5)).         -   For each chroma sample location (xC=0 . . . sbWidth−1, yC=0             . . . sbHeight−1) inside the prediction chroma sample arrays             predSamplesLX, the corresponding prediction chroma sample             value predSamplesLX[xC][yC] is derived as follows:             -   Let (refxSb_(C), refySb_(C)) and (refx_(C), refy_(C)) be                 chroma locations pointed to by a motion vector (mvLX[0],                 mvLX[1]) given in 1/32-sample units. The variables                 refxSb_(C), refySb_(C), refx_(C) and refy_(C) are                 derived as follows:                 refxSb_(C)=((xSb/SubWidthC<<5)+mvLX[0])*hori_scale_fp  (8-763)                 refx                 _(C)=((Sign(refxSb_(C))*((Abs(refxSb_(C))+256)>>9)+xC*((hori_scale_fp+8)>>4))+16)>>5  (8-764)                 refySb_(C)=((ySb/SubHeightC<<5)+mvLX[1])*vert_scale_fp  (8-765)                 refy                 _(C)=((Sign(refySb_(C))*((Abs(refySb_(C))+256)>>9)+yC*((vert_scale_fp+8)>>4))+16)>>5  (8-766)             -   The variables xInt_(C), yInt_(C), xFrac_(C) and                 yFrac_(C) are derived as follows:                 xInt_(C)=                   (8-767)                 yInt_(C)=                   (8-768)                 xFrac_(C)=refy _(C)&31  (8-769)                 yFrac_(C)=refy _(C)&31  (8-770)         -   The prediction sample value predSamplesLX[xC][yC] is derived             by invoking the process specified in clause 8.5.6.3.4 with             (xIntC, yIntC), (xFracC, yFracC), (xSbIntC, ySbIntC),             sbWidth, sbHeight and refPicLX as inputs.

5.6. Embodiment 2 of Reference Sample Position Clipping

8.5.6.3.1 General

Inputs to this process are:

-   -   a luma location (xSb, ySb) specifying the top-left sample of the         current coding subblock relative to the top-left luma sample of         the current picture,     -   a variable sbWidth specifying the width of the current coding         subblock,     -   a variable sbHeight specifying the height of the current coding         subblock,     -   a motion vector offset mvOffset,     -   a refined motion vector refMvLX,     -   the selected reference picture sample array refPicLX,     -   the half sample interpolation filter index hpelIfIdx,     -   the bi-directional optical flow flag bdofFlag,     -   a variable cIdx specifying the colour component index of the         current block.

Outputs of this process are:

-   -   an (sbWidth+brdExtSize)×(sbHeight+brdExtSize) array         predSamplesLX of prediction sample values.

The prediction block border extension size brdExtSize is derived as follows: brdExtSize=(bdofFlag∥(inter_affine_flag[xSb][ySb]&&sps_affine_prof_enabled_flag))?2:0  (8-752)

The variable fRefWidth is set equal to the PicOutputWidthL of the reference picture in luma samples.

The variable fRefHeight is set equal to PicOutputHeightL of the reference picture in luma samples.

The motion vector mvLX is set equal to (refMvLX−mvOffset).

-   -   If cIdx is equal to 0, the following applies:         -   The scaling factors and their fixed-point representations             are defined as             hori_scale_fp=((fRefWidth<<14)+(PicOutputWidthL>>1))/PicOutputWidthL  (8-753)             vert_scale_fp=((fRefHeight<<14)+(PicOutputHeightL>>1))/PicOutputHeightL  (8-754)         -   Let (xIntL, yIntL) be a luma location given in full-sample             units and (xFracL, yFracL) be an offset given in 1/16-sample             units. These variables are used only in this clause for             specifying fractional-sample locations inside the reference             sample arrays refPicLX.         -   The top-left coordinate of the bounding block for reference             sample padding (xSbInt_(L), ySbInt_(L)) is set equal to             (xSb+(mvLX[0]>>4), ySb+(mvLX[1]>>4)).         -   For each luma sample location (x_(L)=0 . . .             sbWidth−1+brdExtSize, y_(L)=0 . . . sbHeight−1+brdExtSize)             inside the prediction luma sample array predSamplesLX, the             corresponding prediction luma sample value             predSamplesLX[x_(L)][y_(L)] is derived as follows:             -   Let (refxSb_(L), refySb_(L)) and (refx_(L), refy_(L)) be                 luma locations pointed to by a motion vector                 (refMvLX[0], refMvLX[1]) given in 1/16-sample units. The                 variables refxSb_(L), refx_(L), refySb_(L), and refx_(L)                 are derived as follows:                 refxSb_(L)=((xSb<<4)+refMvLX[0])*hori_scale_fp  (8-755)                 refx                 _(L)=((Sign(refxSb)*((Abs(refxSb)+128)>>8)+xL*((hori_scale_fp+8)>>4))+32)>>6  (8-756)                 refySb_(L)=((ySb<<4)+refMvLX[1])*vert_scale_fp  (8-757)                 refyL=((Sign(refySb)*((Abs(refySb)+128)>>8)+yL*((vert_scale_fp+8)>>4))+32)>>6  (8-758)             -   The variables xInt_(L), yInt_(L), xFrac_(L) and                 yFrac_(L) are derived as follows:                 xInt_(L)=                   (8-759)                 yInt_(L)=                   (8-760)                 xFrac_(L)=refx _(L)&15  (8-761)                 yFrac_(L)=refy _(L)&15  (8-762)         -   If bdofFlag is equal to TRUE or             (sps_affine_prof_enabled_flag is equal to TRUE and             inter_affine_flag[xSb][ySb] is equal to TRUE), and one or             more of the following conditions are true, the prediction             luma sample value predSamplesLX[x_(L)][y_(L)] is derived by             invoking the luma integer sample fetching process as             specified in clause 8.5.6.3.3 with             (xInt_(L)+(xFrac_(L)>>3)−1), yInt_(L)+(yFrac_(L)>>3)−1) and             refPicLX as inputs.             -   x_(L) is equal to 0.             -   x_(L) is equal to sbWidth+1.             -   y_(L) is equal to 0.             -   y_(L) is equal to sbHeight+1.         -   Otherwise, the prediction luma sample value             predSamplesLX[xL][yL] is derived by invoking the luma sample             8-tap interpolation filtering process as specified in clause             8.5.6.3.2 with (xIntL−(brdExtSize>0?1:0),             yIntL−(brdExtSize>0?1:0)), (xFracL, yFracL), (xSbInt_(L),             ySbInt_(L)), refPicLX, hpelIfIdx, sbWidth, sbHeight and             (xSb, ySb) as inputs.     -   Otherwise (cIdx is not equal to 0), the following applies:         -   Let (xIntC, yIntC) be a chroma location given in full-sample             units and (xFracC, yFracC) be an offset given in 1/32 sample             units. These variables are used only in this clause for             specifying general fractional-sample locations inside the             reference sample arrays refPicLX.         -   The top-left coordinate of the bounding block for reference             sample padding (xSbIntC, ySbIntC) is set equal to             ((xSb/SubWidthC)+(mvLX[0]>>5),             (ySb/SubHeightC)+(mvLX[1]>>5)).         -   For each chroma sample location (xC=0 . . . sbWidth−1, yC=0             . . . sbHeight−1) inside the prediction chroma sample arrays             predSamplesLX, the corresponding prediction chroma sample             value predSamplesLX[xC][yC] is derived as follows:             -   Let (refxSb_(C), refySb_(C)) and (refx_(C), refy_(C)) be                 chroma locations pointed to by a motion vector (mvLX[0],                 mvLX[1]) given in 1/32-sample units. The variables                 refxSb_(C), refySb_(C), refx_(C) and refy_(C) are                 derived as follows:                 refxSb_(C)=((xSb/SubWidthC<<5)+mvLX[0])*hori_scale_fp  (8-763)                 refx                 _(C)=((Sign(refxSb_(C))*((Abs(refxSb_(C))+256)>>9)+xC*((hori_scale_fp+8)>>4))+16)>>5  (8-764)                 refySb_(C)=((ySb/SubHeightC<<5)+mvLX[1])*vert_scale_fp  (8-765)                 refy                 _(C)=((Sign(refySb_(C))*((Abs(refySb_(C))+256)>>9)+yC*((vert_scale_fp+8)>>4))+16)>>5  (8-766)             -   The variables xInt_(C), yInt_(C), xFrac_(C) and                 yFrac_(C) are derived as follows:                 xInt_(C)=                    (8-767)                 yInt_(C)=                    (8-768)                 xFrac_(C)=refy _(C)&31  (8-769)                 yFrac_(C)=refy _(C)&31  (8-770)         -   The prediction sample value predSamplesLX[xC][yC] is derived             by invoking the process specified in clause 8.5.6.3.4 with             (xIntC, yIntC), (xFracC, yFracC), (xSbIntC, ySbIntC),             sbWidth, sbHeight and refPicLX as inputs.

5.7. Embodiment of Usage of Coding Tools

5.7.1 BDOF on/Off Control

-   -   The variable currPic specifies the current picture and the         variable bdofFlag is derived as follows:         -   If all of the following conditions are true, bdofFlag is set             equal to TRUE.             -   sps_bdof_enabled_flag is equal to 1 and                 slice_disable_bdof_dmvr_flag is equal to 0.

            -   predFlagL0[xSbIdx][ySbIdx] and                 predFlagL1[xSbIdx][ySbIdx] are both equal to 1.

            -   DiffPicOrderCnt(currPic, RefPicList[0][refIdxL0]) is                 equal to DiffPicOrderCnt(RefPicList[1][refIdxL1],                 currPic).

            -   RefPicList[0][refIdxL0] is a short-term reference                 picture and RefPicList[1][refIdxL1] is a short-term                 reference picture.

            -   MotionModelIdc[xCb][yCb] is equal to 0.

            -   merge_subblock_flag[xCb][yCb] is equal to 0.

            -   sym_mvd_flag[xCb][yCb] is equal to 0.

            -   ciip_flag[xCb][yCb] is equal to 0.

            -   BcwIdx[xCb][yCb] is equal to 0.

            -   luma_weight_l0_flag[refIdxL0] and luma                 weight_l1_flag[refIdxL1] are both equal to 0.

            -   cbWidth is greater than or equal to 8.

            -   cbHeight is greater than or equal to 8.

            -   cbHeight*cbWidth is greater than or equal to 128.

            -   

            -   cIdx is equal to 0.         -   Otherwise, bdofFlag is set equal to FALSE.

5.7.2 DMVR on/Off Control

-   -   When all of the following conditions are true, dmvrFlag is set         equal to 1:         -   sps_dmvr_enabled_flag is equal to 1 and             slice_disable_bdof_dmvr_flag is equal to 0

        -   general_merge_flag[xCb][yCb] is equal to 1

        -   both predFlagL0[0][0] and predFlagL1[0][0] are equal to 1

        -   mmvd_merge_flag[xCb][yCb] is equal to 0

        -   ciip_flag[xCb][yCb] is equal to 0

        -   DiffPicOrderCnt(currPic, RefPicList[0][refIdxL0]) is equal             to DiffPicOrderCnt(RefPicList[1][refIdxL1], currPic)

        -   RefPicList[0][refIdxL0] is a short-term reference picture             and RefPicList[1][refIdxL1] is a short-term reference             picture.

        -   BcwIdx[xCb][yCb] is equal to 0

        -   Both luma_weight_l0_flag[refIdxL0] and             luma_weight_l1_flag[refIdxL1] are equal to 0

        -   cbWidth is greater than or equal to 8

        -   cbHeight is greater than or equal to 8

        -   cbHeight*cbWidth is greater than or equal to 128

        -   

5.7.3 PROF on/Off Control for a Reference Picture List X

The variable cbProfFlagLX is derived as follows:

-   -   If one or more of the following conditions are true,         cbProfFlagLX is set equal to FALSE.         -   sps_affine_prof_enabled_flag is equal to 0.

        -   fallbackModeTriggered is equal to 1.

        -   numCpMv is equal to 2 and cpMvLX[1][0] is equal to             cpMvLX[0][0] and cpMvLX[1][1] is equal to cpMvLX[0][1].

        -   numCpMv is equal to 3 and cpMvLX[1][0] is equal to             cpMvLX[0][0] and cpMvLX[1][1] is equal to cpMvLX[0][1] and             cpMvLX[2][0] is equal to cpMvLX[0][0] and cpMvLX[2][1] is             equal to cpMvLX[0][1].

        -   

        -   [[The pic_width_in_luma_samples of the reference picture             refPicLX associated with the refIdxLX is not equal to the             pic_width_in_luma_samples of the current picture,             respectively.

        -   The pic_height_in_luma_samples of the reference picture             refPicLX associated with the refIdxLX is not equal to the             pic_height_in_luma_samples of the current picture,             respectively.]]     -   Otherwise, cbProfFlagLX set equal to TRUE.

5.7.4 PROF on/Off Control for a Reference Picture List X (a Second Embodiment)

The variable cbProfFlagLX is derived as follows:

-   -   If one or more of the following conditions are true,         cbProfFlagLX is set equal to FALSE.         -   sps_affine_prof_enabled_flag is equal to 0.

        -   fallbackModeTriggered is equal to 1.

        -   numCpMv is equal to 2 and cpMvLX[1][0] is equal to             cpMvLX[0][0] and cpMvLX[1][1] is equal to cpMvLX[0][1].

        -   numCpMv is equal to 3 and cpMvLX[1][0] is equal to             cpMvLX[0][0] and cpMvLX[1][1] is equal to cpMvLX[0][1] and             cpMvLX[2][0] is equal to cpMvLX[0][0] and cpMvLX[2][1] is             equal to cpMvLX[0][1].

        -   

        -   [[The pic_width_in_luma_samples of the reference picture             refPicLX associated with the refIdxLX is not equal to the             pic_width_in_luma_samples of the current picture,             respectively.

        -   The pic_height_in_luma_samples of the reference picture             refPicLX associated with the refIdxLX is not equal to the             pic_height_in_luma_samples of the current picture,             respectively.]]     -   Otherwise, cbProfFlagLX set equal to TRUE.

6. Example Implementations of the Disclosed Technology

FIG. 5 is a block diagram of a video processing apparatus 500. The apparatus 500 may be used to implement one or more of the methods described herein. The apparatus 500 may be embodied in a smartphone, tablet, computer, Internet of Things (IoT) receiver, and so on. The apparatus 500 may include one or more processors 502, one or more memories 504 and video processing hardware 506. The processor(s) 502 may be configured to implement one or more methods described in the present document. The memory (memories) 504 may be used for storing data and code used for implementing the methods and techniques described herein. The video processing hardware 506 may be used to implement, in hardware circuitry, some techniques described in the present document, and may be partly or completely be a part of the processors 502 (e.g., graphics processor core GPU or other signal processing circuitry).

In the present document, the term “video processing” or coding may refer to video encoding, video decoding, video compression or video decompression. For example, video compression algorithms may be applied during conversion from pixel representation of a video to a corresponding bitstream representation or vice versa. The bitstream representation of a current video block may, for example, correspond to bits that are either co-located or spread in different places within the bitstream, as is defined by the syntax. For example, a macroblock may be encoded in terms of transformed and coded error residual values and also using bits in headers and other fields in the bitstream.

It will be appreciated that the disclosed methods and techniques will benefit video encoder and/or decoder embodiments incorporated within video processing devices such as smartphones, laptops, desktops, and similar devices by allowing the use of the techniques disclosed in the present document.

FIG. 6 is a flowchart for an example method 600 of video processing. The method 600 includes, at 610, performing a conversion between a current video block and a coded representation of the current video block, wherein, during the conversion, if a resolution and/or a size of a reference picture is different from a resolution and/or a size of the current video block, a same interpolation filter is applied to a group ofadjacentornon-adjacentsamplespredictedusingthecurrentvideoblock.

Some embodiments may be described using the following clause-based format.

1. A method of video processing, comprising:

-   -   performing a conversion between a current video block and a         coded representation of the current video block, wherein, during         the conversion, if a resolution and/or a size of a reference         picture is different from a resolution and/or a size of the         current video block, a same interpolation filter is applied to a         group of adjacent or non-adjacent samples predicted using the         current video block.

2. The method of clause 1, wherein the same interpolation filter is a vertical interpolation filter.

3. The method of clause 1, wherein the same interpolation filter is a horizontal interpolation filter.

4. The method of clause 1, wherein the group of adjacent or non-adjacent samples include all samples located in a region of the current video block.

5. The method of clause 4, wherein the current video blocks is divided into multiple rectangles each of size M×N.

6. The method of clause 5, wherein M and/or N are pre-determined.

7. The method of clause 5, wherein M and/or N are derived from dimensions of the current video block.

8. The method of clause 5, wherein M and/or N are signaled in the coded representation of the current video block.

9. The method of clause 1, wherein the group of samples share a same motion vector.

10. The method of clause 9, wherein the group of samples share a same horizontal component and/or a same fractional part of a horizontal component.

11. The method of clause 9, wherein the group of samples share a same vertical component and/or a same fractional part of a vertical component.

12. The method of one or more of clauses 9-11, wherein the same motion vector or components thereof satisfy one or more rules based at least on one of: the resolution of the reference picture, the size of the reference picture, the resolution of the current video block, the size of the current video block, or a precision value.

13. The method of one or more of clauses 9-11, wherein the same motion vector or components thereof corresponds to a motion information of a sample located in the current video block.

14. The method of one or more of clauses 9-11, wherein the same motion vector or components thereof are set to a motion information of a virtual sample located inside or outside the group.

15. A method of video processing, comprising:

-   -   performing a conversion between a current video block and a         coded representation of the current video block, wherein, during         the conversion, if a resolution and/or a size of a reference         picture is different from a resolution and/or a size of the         current video block, wherein blocks predicted using the current         video block are only allowed to use integer-valued motion         information related to the current block.

16. The method of clause 15, wherein the integer-valued motion information is derived by rounding an original motion information of the current video block.

17. The method of clause 15, wherein the original motion information of the current video block is in a horizontal direction and/or a vertical direction.

18. A method of video processing, comprising:

-   -   performing a conversion between a current video block and a         coded representation of the current video block, wherein, during         the conversion, if a resolution and/or a size of a reference         picture is different from a resolution and/or a size of the         current video block, an interpolation filter is applied to         derive blocks predicted using the current video block, and         wherein the interpolation filter is selected based on a rule.

19. The method of clause 18, whether the rule is related to the resolution and/or the size of the reference picture relative to the resolution and/or the size of the current video block.

20. The method of clause 18, wherein the interpolation filter is a vertical interpolation filter.

21. The method of clause 18, wherein the interpolation filter is a horizontal interpolation filter.

22. The method of clause 18, wherein the interpolation filter is one of: a 1-tap filter, a bilinear filter, a 4-tap filter, or a 6-tap filter.

23. The method of clause 22, wherein the interpolation filter is used as part of other steps of the conversion.

24. The method of clause 18, wherein the interpolation filter includes a use of padding samples.

25. The method of clause 18, wherein a use of the interpolation filter depends on a color component of a sample of the current video block.

26. A method of video processing, comprising:

-   -   performing a conversion between a current video block and a         coded representation of the current video block, wherein, during         the conversion, if a resolution and/or a size of a reference         picture is different from a resolution and/or a size of the         current video block, selectively applying a deblocking filter,         wherein a strength of the deblocking filter set in accordance         with a rule related to the resolution and/or the size of the         reference picture relative to the resolution and/or the size of         the current video block.

27. The method of clause 27, wherein the strength of the deblocking filter varies from one video block to another.

28. A method of video processing, comprising:

-   -   performing a conversion between a current video block and a         coded representation of the current video block, wherein, during         the conversion, if a sub-picture of the current video block         exists, a conformance bitstream satisfies a rule related to the         resolution and/or the size of the reference picture relative to         the resolution and/or the size of the current video block.

29. The method of clause 28, further comprising:

-   -   splitting the current video block into one or more sub-pictures,         wherein the splitting depends at least on the resolution of the         current video block.

30. A method of video processing, comprising:

-   -   performing a conversion between a current video block and a         coded representation of the current video block, wherein, during         the conversion, a reference picture of the current video block         is resampled in accordance with a rule based on dimensions of         the current video block.

31. A method of video processing, comprising:

-   -   performing a conversion between a current video block and a         coded representation of the current video block, wherein, during         the conversion, a use of a coding tool on the current video         block is selectively enabled or disabled depending on a         resolution/size of a reference picture of the current video         block relative to a resolution/size of the current video block.

32. The method of one or more of the aforementioned clauses, wherein the group of samples are located in a conformance window.

33. The method of clause 32, wherein the conformance window is rectangular in shape.

34. The method of any one or more of the aforementioned clauses, wherein the resolution pertains to a resolution of the coded/decoded video block or a resolution of the conformance window in the coded/decoded video block.

35. The method of any one or more of the aforementioned clauses, wherein the size pertains to a size of the coded/decoded video block or a size of the conformance window in the coded/decoded video block.

36. The method of any one or more of the aforementioned clauses, wherein the dimensions pertain to dimensions of the coded/decoded video block or dimensions of the conformance window in the coded/decoded video block.

37. The method of clause 32, wherein the conformance window is defined by a set of conformance cropping window parameters.

38. The method of clause 37, wherein at least a portion of set of conformance cropping window parameters are implicitly or explicitly signaled in the coded representation.

39. The method of any one or more of the aforementioned clauses, wherein the set of conformance cropping window parameters is disallowed to be signaled in the coded representation.

40. The method of any one or more of the aforementioned clauses, wherein a position of the reference sample is derived with respect to a top-left sample of the current video block in the conformance window.

41. A method of video processing, comprising:

-   -   performing a conversion between multiple video blocks and coded         representations of the multiple video blocks, wherein, during         the conversion, a first conformance window is defined for a         first video block and a second conformance window for a second         video block, and wherein a ratio of a width and/or a height of         the first conformance window to the second conformance window is         in accordance with a rule based at least on a conformance         bitstream.

42. A video decoding apparatus comprising a processor configured to implement a method recited in one or more of clauses 1 to 41.

43. A video encoding apparatus comprising a processor configured to implement a method recited in one or more of clauses 1 to 41.

44. A computer program product having computer code stored thereon, the code, when executed by a processor, causes the processor to implement a method recited in any of clauses 1 to 41.

45. A method, apparatus or system described in the present document.

FIG. 9 is a block diagram showing an example video processing system 900 in which various techniques disclosed herein may be implemented. Various implementations may include some or all of the components of the system 900. The system 900 may include input 902 for receiving video content. The video content may be received in a raw or uncompressed format, e.g., 8 or 10 bit multi-component pixel values, or may be in a compressed or encoded format. The input 902 may represent a network interface, a peripheral bus interface, or a storage interface. Examples of network interface include wired interfaces such as Ethernet, passive optical network (PON), etc. and wireless interfaces such as Wi-Fi or cellular interfaces.

The system 900 may include a coding component 904 that may implement the various coding or encoding methods described in the present document. The coding component 904 may reduce the average bitrate of video from the input 902 to the output of the coding component 904 to produce a coded representation of the video. The coding techniques are therefore sometimes called video compression or video transcoding techniques. The output of the coding component 904 may be either stored, or transmitted via a communication connected, as represented by the component 906. The stored or communicated bitstream (or coded) representation of the video received at the input 902 may be used by the component 908 for generating pixel values or displayable video that is sent to a display interface 910. The process of generating user-viewable video from the bitstream representation is sometimes called video decompression. Furthermore, while certain video processing operations are referred to as “coding” operations or tools, it will be appreciated that the coding tools or operations are used at an encoder and corresponding decoding tools or operations that reverse the results of the coding will be performed by a decoder.

Examples of a peripheral bus interface or a display interface may include universal serial bus (USB) or high definition multimedia interface (HDMI) or Displayport, and so on. Examples of storage interfaces include SATA (serial advanced technology attachment), PCI, IDE interface, and the like. The techniques described in the present document may be embodied in various electronic devices such as mobile phones, laptops, smartphones or other devices that are capable of performing digital data processing and/or video display.

FIG. 10 is a block diagram that illustrates an example video coding system 100 that may utilize the techniques of this disclosure.

As shown in FIG. 10 , video coding system 100 may include a source device 110 and a destination device 120. Source device 110 generates encoded video data which may be referred to as a video encoding device. Destination device 120 may decode the encoded video data generated by source device 110 which may be referred to as a video decoding device.

Source device 110 may include a video source 112, a video encoder 114, and an input/output (I/O) interface 116.

Video source 112 may include a source such as a video capture device, an interface to receive video data from a video content provider, and/or a computer graphics system for generating video data, or a combination of such sources. The video data may comprise one or more pictures. Video encoder 114 encodes the video data from video source 112 to generate a bitstream. The bitstream may include a sequence of bits that form a coded representation of the video data. The bitstream may include coded pictures and associated data. The coded picture is a coded representation of a picture. The associated data may include sequence parameter sets, picture parameter sets, and other syntax structures. I/O interface 116 may include a modulator/demodulator (modem) and/or a transmitter. The encoded video data may be transmitted directly to destination device 120 via I/O interface 116 through network 130 a. The encoded video data may also be stored onto a storage medium/server 130 b for access by destination device 120.

Destination device 120 may include an I/O interface 126, a video decoder 124, and a display device 122.

I/O interface 126 may include a receiver and/or a modem. I/O interface 126 may acquire encoded video data from the source device 110 or the storage medium/server 130 b. Video decoder 124 may decode the encoded video data. Display device 122 may display the decoded video data to a user. Display device 122 may be integrated with the destination device 120, or may be external to destination device 120 which be configured to interface with an external display device.

Video encoder 114 and video decoder 124 may operate according to a video compression standard, such as the High Efficiency Video Coding (HEVC) standard, Versatile Video Coding (VVC) standard and other current and/or further standards.

FIG. 11 is a block diagram illustrating an example of video encoder 200, which may be video encoder 114 in the system 100 illustrated in FIG. 10 .

Video encoder 200 may be configured to perform any or all of the techniques of this disclosure. In the example of FIG. 9 , video encoder 200 includes a plurality of functional components. The techniques described in this disclosure may be shared among the various components of video encoder 200. In some examples, a processor may be configured to perform any or all of the techniques described in this disclosure.

The functional components of video encoder 200 may include a partition unit 201, a predication unit 202 which may include a mode select unit 203, a motion estimation unit 204, a motion compensation unit 205 and an intra prediction unit 206, a residual generation unit 207, a transform unit 208, a quantization unit 209, an inverse quantization unit 210, an inverse transform unit 211, a reconstruction unit 212, a buffer 213, and an entropy encoding unit 214.

In other examples, video encoder 200 may include more, fewer, or different functional components. In an example, predication unit 202 may include an intra block copy (IBC) unit. The IBC unit may perform predication in an IBC mode in which at least one reference picture is a picture where the current video block is located.

Furthermore, some components, such as motion estimation unit 204 and motion compensation unit 205 may be highly integrated, but are represented in the example of FIG. 5 separately for purposes of explanation.

Partition unit 201 may partition a picture into one or more video blocks. Video encoder 200 and video decoder 300 may support various video block sizes.

Mode select unit 203 may select one of the coding modes, intra or inter, e.g., based on error results, and provide the resulting intra- or inter-coded block to a residual generation unit 207 to generate residual block data and to a reconstruction unit 212 to reconstruct the encoded block for use as a reference picture. In some example, Mode select unit 203 may select a combination of intra and inter predication (CIIP) mode in which the predication is based on an inter predication signal and an intra predication signal. Mode select unit 203 may also select a resolution for a motion vector (e.g, a sub-pixel or integer pixel precision) for the block in the case of inter-predication.

To perform inter prediction on a current video block, motion estimation unit 204 may generate motion information for the current video block by comparing one or more reference frames from buffer 213 to the current video block. Motion compensation unit 205 may determine a predicted video block for the current video block based on the motion information and decoded samples of pictures from buffer 213 other than the picture associated with the current video block.

Motion estimation unit 204 and motion compensation unit 205 may perform different operations for a current video block, for example, depending on whether the current video block is in an I slice, a P slice, or a B slice.

In some examples, motion estimation unit 204 may perform uni-directional prediction for the current video block, and motion estimation unit 204 may search reference pictures of list 0 or list 1 for a reference video block for the current video block. Motion estimation unit 204 may then generate a reference index that indicates the reference picture in list 0 or list 1 that contains the reference video block and a motion vector that indicates a spatial displacement between the current video block and the reference video block. Motion estimation unit 204 may output the reference index, a prediction direction indicator, and the motion vector as the motion information of the current video block. Motion compensation unit 205 may generate the predicted video block of the current block based on the reference video block indicated by the motion information of the current video block.

In other examples, motion estimation unit 204 may perform bi-directional prediction for the current video block, motion estimation unit 204 may search the reference pictures in list 0 for a reference video block for the current video block and may also search the reference pictures in list 1 for another reference video block for the current video block. Motion estimation unit 204 may then generate reference indexes that indicate the reference pictures in list 0 and list 1 containing the reference video blocks and motion vectors that indicate spatial displacements between the reference video blocks and the current video block. Motion estimation unit 204 may output the reference indexes and the motion vectors of the current video block as the motion information of the current video block. Motion compensation unit 205 may generate the predicted video block of the current video block based on the reference video blocks indicated by the motion information of the current video block.

In some examples, motion estimation unit 204 may output a full set of motion information for decoding processing of a decoder.

In some examples, motion estimation unit 204 may do not output a full set of motion information for the current video. Rather, motion estimation unit 204 may signal the motion information of the current video block with reference to the motion information of another video block. For example, motion estimation unit 204 may determine that the motion information of the current video block is sufficiently similar to the motion information of a neighboring video block.

In one example, motion estimation unit 204 may indicate, in a syntax structure associated with the current video block, a value that indicates to the video decoder 300 that the current video block has the same motion information as the another video block.

In another example, motion estimation unit 204 may identify, in a syntax structure associated with the current video block, another video block and a motion vector difference (MVD). The motion vector difference indicates a difference between the motion vector of the current video block and the motion vector of the indicated video block. The video decoder 300 may use the motion vector of the indicated video block and the motion vector difference to determine the motion vector of the current video block.

As discussed above, video encoder 200 may predictively signal the motion vector. Two examples of predictive signaling techniques that may be implemented by video encoder 200 include advanced motion vector predication (AMVP) and merge mode signaling.

Intra prediction unit 206 may perform intra prediction on the current video block. When intra prediction unit 206 performs intra prediction on the current video block, intra prediction unit 206 may generate prediction data for the current video block based on decoded samples of other video blocks in the same picture. The prediction data for the current video block may include a predicted video block and various syntax elements.

Residual generation unit 207 may generate residual data for the current video block by subtracting (e.g., indicated by the minus sign) the predicted video block(s) of the current video block from the current video block. The residual data of the current video block may include residual video blocks that correspond to different sample components of the samples in the current video block.

In other examples, there may be no residual data for the current video block for the current video block, for example in a skip mode, and residual generation unit 207 may not perform the subtracting operation.

Transform processing unit 208 may generate one or more transform coefficient video blocks for the current video block by applying one or more transforms to a residual video block associated with the current video block.

After transform processing unit 208 generates a transform coefficient video block associated with the current video block, quantization unit 209 may quantize the transform coefficient video block associated with the current video block based on one or more quantization parameter (QP) values associated with the current video block.

Inverse quantization unit 210 and inverse transform unit 211 may apply inverse quantization and inverse transforms to the transform coefficient video block, respectively, to reconstruct a residual video block from the transform coefficient video block. Reconstruction unit 212 may add the reconstructed residual video block to corresponding samples from one or more predicted video blocks generated by the predication unit 202 to produce a reconstructed video block associated with the current block for storage in the buffer 213.

After reconstruction unit 212 reconstructs the video block, loop filtering operation may be performed reduce video blocking artifacts in the video block.

Entropy encoding unit 214 may receive data from other functional components of the video encoder 200. When entropy encoding unit 214 receives the data, entropy encoding unit 214 may perform one or more entropy encoding operations to generate entropy encoded data and output a bitstream that includes the entropy encoded data.

FIG. 12 is a block diagram illustrating an example of video decoder 300 which may be video decoder 114 in the system 100 illustrated in FIG. 10 .

The video decoder 300 may be configured to perform any or all of the techniques of this disclosure. In the example of FIG. 10 , the video decoder 300 includes a plurality of functional components. The techniques described in this disclosure may be shared among the various components of the video decoder 300. In some examples, a processor may be configured to perform any or all of the techniques described in this disclosure.

In the example of FIG. 10 , video decoder 300 includes an entropy decoding unit 301, a motion compensation unit 302, an intra prediction unit 303, an inverse quantization unit 304, an inverse transformation unit 305, and a reconstruction unit 306 and a buffer 307. Video decoder 300 may, in some examples, perform a decoding pass generally reciprocal to the encoding pass described with respect to video encoder 200 (e.g., FIG. 9 ).

Entropy decoding unit 301 may retrieve an encoded bitstream. The encoded bitstream may include entropy coded video data (e.g., encoded blocks of video data). Entropy decoding unit 301 may decode the entropy coded video data, and from the entropy decoded video data, motion compensation unit 302 may determine motion information including motion vectors, motion vector precision, reference picture list indexes, and other motion information. Motion compensation unit 302 may, for example, determine such information by performing the AMVP and merge mode.

Motion compensation unit 302 may produce motion compensated blocks, possibly performing interpolation based on interpolation filters. Identifiers for interpolation filters to be used with sub-pixel precision may be included in the syntax elements.

Motion compensation unit 302 may use interpolation filters as used by video encoder 20 during encoding of the video block to calculate interpolated values for sub-integer pixels of a reference block. Motion compensation unit 302 may determine the interpolation filters used by video encoder 200 according to received syntax information and use the interpolation filters to produce predictive blocks.

Motion compensation unit 302 may uses some of the syntax information to determine sizes of blocks used to encode frame(s) and/or slice(s) of the encoded video sequence, partition information that describes how each macroblock of a picture of the encoded video sequence is partitioned, modes indicating how each partition is encoded, one or more reference frames (and reference frame lists) for each inter-encoded block, and other information to decode the encoded video sequence.

Intra prediction unit 303 may use intra prediction modes for example received in the bitstream to form a prediction block from spatially adjacent blocks. Inverse quantization unit 303 inverse quantizes, e.g., de-quantizes, the quantized video block coefficients provided in the bitstream and decoded by entropy decoding unit 301. Inverse transform unit 303 applies an inverse transform.

Reconstruction unit 306 may sum the residual blocks with the corresponding prediction blocks generated by motion compensation unit 202 or intra-prediction unit 303 to form decoded blocks. If desired, a deblocking filter may also be applied to filter the decoded blocks in order to remove blockiness artifacts. The decoded video blocks are then stored in buffer 307, which provides reference blocks for subsequent motion compensation.

FIG. 11 is a flowchart representation of a method of video processing in accordance with the present technology. The method 1100 includes, at operation 1110, performing a conversion between a video and a bitstream representation of the video. The bitstream representation conforms to a format rule that specifies that applicability of a Decoder-side Motion Vector Refinement coding tool and a Bi-Directional Optical Flow coding tool for the video picture are indicated separately in the bitstream representation.

FIG. 13 is a flowchart representation of a method 1300 of video processing in accordance with the present technology. The method 1300 includes, at operation 1310, determining for a conversion between a current picture of a video and a bitstream representation of the video, usage of a coding tool based on a condition associated with a dimension of a portion of one of multiple reference pictures or the current picture. The method 1300 also includes, at operation 1320, performing the conversion based on the determining.

In some embodiments, the usage comprises whether the coding tool is enabled for the current picture. In some embodiments, the portion of a picture comprises a conformance window outside of which samples are disposable when outputting the video, a scaling window in which samples are subject to a resampling operation, or an entirely of the picture. In some embodiments, the coding tool comprises a Decoder-side Motion Vector Refinement coding tool, a Bi-Directional Optical Flow coding tool, a prediction refinement with optical flow (PROF) coding tool, or an interpolation filter with a half-pel precision for motion compensation. In some embodiments, the coding tool further comprises a temporal motion vector prediction coding tool, a multiple transform sets coding tool, a cross-component adaptive loop filtering coding tool, a geometric partitioning coding tool, a blending process for a coding tool that splits a block into multiple partitions, a coding tool that requires stored information in a picture different than the current picture, a coding tool that generates a pairwise merge candidate, a bi-prediction with coding-unit level weights, a weighted prediction coding tool, an affine prediction coding tool, or an adaptive motion vector resolution coding tool.

In some embodiments, the coding tool is disabled in case the condition specifying the dimension in the portion of at least one of the multiple reference pictures is different than a dimension of the current picture is satisfied. In some embodiments, the dimension of the portion is modified for the determining. In some embodiments, the usage of the coding tool is based on at least one of (1) a width of the picture minus one or more horizontal offsets, or (2) a height of the picture minus one or more vertical offsets. In some embodiments, the one or more horizontal offsets comprise a left offset for a scaling window. In some embodiments, the one or more vertical offsets comprise a top offset fora scaling window. In some embodiments, the one or more horizontal offsets comprise a right offset and a left offset for a scaling window. In some embodiments, the one or more vertical offsets comprise a bottom offset and top offset for a scaling window. In some embodiments, the one or more horizontal offsets comprise a value based on scaling a sum of aright offset and a left offset for a scaling window. In some embodiments, the one or more vertical offsets comprise a value based on scaling a sum of a bottom offset and top offset fora scaling window.

In some embodiments, the coding tool is disabled in case the condition specifying dimensions of portions of at least two of the multiple reference pictures are different is satisfied. In some embodiments, a first pairwise merge candidate is marked as unavailable in case dimensions of portions of at least two of the multiple reference pictures used to derive the first pairwise merge candidate for one or two reference picture lists are different. In some embodiments, the syntax element indicating the usage of the coding tool is conditionally signaled in the bitstream representation based on the dimensions of the portions. In some embodiments, the syntax element indicating the usage of the coding tool is omitted in the bitstream representation.

In some embodiments, the syntax element indicating the usage of the coding tool is conditionally included in the bitstream representation further based on whether a reference picture resampling (RPR) process is enabled. In some embodiments, the syntax element comprising one of amvr_precision_idx, sym_mvd_flag, or mmvd_merge_flag. In some embodiments, the conversion according to the usage of the coding tool is modified based on the dimensions of the portions. In some embodiments, the conversion comprises deriving a motion vector difference for a reference picture list in a symmetric motion vector difference process, the deriving is based on a difference of dimensions of portions of at least two of the multiple reference pictures. In some embodiments, the conversion comprises deriving a pairwise merge candidate, and the deriving comprises applying a weighted average based on a difference of dimensions of portions of at least two of the multiple reference pictures.

FIG. 14 is a flowchart representation of a method 1400 of video processing in accordance with the present technology. The method 1400 includes, at operation 1410, performing a conversion between a block of a video and a bitstream representation of the video. During the conversion an adaptive motion vector resolution (AMVR) with ½-pel motion vector precision is enabled for the block due to a reference picture resampling process is applicable to the block.

In some embodiments, a different interpolation filter is used for blocks having a precision different than ½-pel precision. In some embodiments, the condition associated with the dimension of the portion of the reference picture is indicated by a flag associated with the reference picture. In some embodiments, the coding tool is disabled in case the flag indicates that at least one reference picture in a reference picture list is scaled. In some embodiments, the flag comprises RefPicIsScaled[0][refIdxL0], wherein refIdxL0 is an index for a first reference picture list. In some embodiments, the flag comprises RefPicIsScaled[0][refIdxL1], wherein refIdxL1 is an index for second first reference picture list. In some embodiments, the flag is determined during a reference picture list construction process.

FIG. 15 is a flowchart representation of a method 1500 of video processing in accordance with the present technology. The method 1500 includes, at operation 1510, determining for a conversion between a block of a video and a bitstream representation of the video, a sum of absolution difference used in a Bi-Directional Optical Flow (BDOF) coding tool or a Decoder-side Motion Vector Refinement (DMVR) coding tool in a manner that is based on a bit-depth of the block. The method 1500 also includes, at operation 1520, performing the conversion based on the determining.

In some embodiments, the sum of absolution difference is shifted based on a function of the bit-depth before being compared to a threshold for the BDOF coding tool or the DMVR coding tool. In some embodiments, the sum of absolution difference is compared to a threshold that is modified based on a function of the bit-depth.

In some embodiments, the conversion includes encoding the video into the bitstream representation. In some embodiments, the conversion includes decoding the bitstream representation into the video.

Some embodiments of the disclosed technology include making a decision or determination to enable a video processing tool or mode. In an example, when the video processing tool or mode is enabled, the encoder will use or implement the tool or mode in the processing of a block of video, but may not necessarily modify the resulting bitstream based on the usage of the tool or mode. That is, a conversion from the block of video to the bitstream representation of the video will use the video processing tool or mode when it is enabled based on the decision or determination. In another example, when the video processing tool or mode is enabled, the decoder will process the bitstream with the knowledge that the bitstream has been modified based on the video processing tool or mode. That is, a conversion from the bitstream representation of the video to the block of video will be performed using the video processing tool or mode that was enabled based on the decision or determination.

Some embodiments of the disclosed technology include making a decision or determination to disable a video processing tool or mode. In an example, when the video processing tool or mode is disabled, the encoder will not use the tool or mode in the conversion of the block of video to the bitstream representation of the video. In another example, when the video processing tool or mode is disabled, the decoder will process the bitstream with the knowledge that the bitstream has not been modified using the video processing tool or mode that was enabled based on the decision or determination.

The disclosed and other solutions, examples, embodiments, modules and the functional operations described in this document can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this document and their structural equivalents, or in combinations of one or more of them. The disclosed and other embodiments can be implemented as one or more computer program products, e.g., one or more modules of computer program instructions encoded on a computer readable medium for execution by, or to control the operation of, data processing apparatus. The computer readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more them. The term “data processing apparatus” encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can include, in addition to hardware, code that creates an execution environment forth computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them. A propagated signal is an artificially generated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal, that is generated to encode information for transmission to suitable receiver apparatus.

A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

The processes and logic flows described in this document can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

Processors suitable forth execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read only memory or a random-access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks. However, a computer need not have such devices. Computer readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto optical disks; and CD ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

While this patent document contains many specifics, these should not be construed as limitations on the scope of any subject matter or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular techniques. Certain features that are described in this patent document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Moreover, the separation of various system components in the embodiments described in this patent document should not be understood as requiring such separation in all embodiments.

Only a few implementations and examples are described and other implementations, enhancements and variations can be made based on what is described and illustrated in this patent document. 

What is claimed is:
 1. A method of video processing, comprising: determining, for a conversion between a current block of a current picture of a video and a bitstream of the video, whether to disable a refinement coding tool for refining a motion vector or a prediction sample for the current block by an offset value; and performing the conversion based on the determining, wherein the refinement coding tool is disabled when a dimension of a reference picture of one or more reference pictures of the current block is different from a dimension of the current picture, or a dimension of a scaling window in a reference picture of one or more reference pictures of the current block is different from a dimension of a scaling window in the current picture.
 2. The method of claim 1, wherein the refinement coding tool comprises a first refinement coding tool, and wherein the first refinement coding tool refines a signaled motion vector based on at least one motion vector with an offset to the signaled motion vector.
 3. The method of claim 1, wherein the refinement coding tool comprises a second refinement coding tool, and wherein the second refinement coding tool obtains a motion vector refinement based on at least one gradient value corresponding to a sample in a reference block of the current block.
 4. The method of claim 1, wherein an affine mode is applied to the current block and initial prediction samples of a sub-block of the current block are generated, wherein the refinement coding tool comprises a third refinement coding tool, wherein the third refinement coding tool is applied to generate final prediction samples for the sub-block by deriving a prediction refinement based on motion vector differences dMvH and/or dMvV, and wherein dMvH and dMvV indicate motion vector differences along a horizontal direction and a vertical direction.
 5. The method of claim 4, wherein the third refinement coding tool is disabled for a first reference picture list of the current block when a dimension of a reference picture in the first reference picture list is different from a dimension of the current picture, or a dimension of a scaling window in a reference picture in the first reference picture list is different from a dimension of a scaling window in the current picture, and wherein the third refinement coding tool is disabled for a second reference picture list of the current block when a dimension of a reference picture in the second reference picture list is different from a dimension of the current picture, or a dimension of a scaling window in a reference picture in the second reference picture list is different from a dimension of a scaling window in the current picture.
 6. The method of claim 1, wherein whether the refinement coding tool is disabled is determined based on values of one or more flags associated with the one or more reference pictures respectively.
 7. The method of claim 6, wherein when a dimension of a reference picture in a first reference picture list of the current block is different from a dimension of the current picture, or a dimension of a scaling window in a reference picture in a first reference picture list of the current block is different from a dimension of a scaling window in the current picture, a value of a first flag is set to be unequal to 0, and when a dimension of a reference picture in a second reference picture list of the current block is different from a dimension of the current picture, or a dimension of a scaling window in a reference picture in a second reference picture list of the current block is different from a dimension of a scaling window in the current picture, a value of a second flag is set to be unequal to
 0. 8. The method of claim 6, wherein the one or more flags are derived during a reference picture list construction process.
 9. The method of claim 1, wherein a dimension of a scaling window is determined based on at least one of a left offset associated with the scaling window, a right offset associated with the scaling window, a bottom offset associated with the scaling window, or a top offset associated with the scaling window.
 10. The method of claim 1, wherein an adaptive motion vector resolution is enabled for the current block when a dimension of a reference picture of one or more reference pictures of the current block is different from a dimension of the current picture, or a dimension of a scaling window in a reference picture of one or more reference pictures of the current block is different from a dimension of a scaling window in the current picture.
 11. The method of claim 1, wherein the conversion includes encoding the current picture into the bitstream.
 12. The method of claim 1, wherein the conversion includes decoding the current picture from the bitstream.
 13. An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to: determine, for a conversion between a current block of a current picture of a video and a bitstream of the video, whether to disable a refinement coding tool for refining a motion vector or a prediction sample for the current block by an offset value; and perform the conversion based on the determining, wherein the refinement coding tool is disabled when a dimension of a reference picture of one or more reference pictures of the current block is different from a dimension of the current picture, or a dimension of a scaling window in a reference picture of one or more reference pictures of the current block is different from a dimension of a scaling window in the current picture.
 14. The apparatus of claim 13, wherein the refinement coding tool comprises a first refinement coding tool, and wherein the first refinement coding tool refines a signaled motion vector based on at least one motion vector with an offset to the signaled motion vector.
 15. The apparatus of claim 13, wherein the refinement coding tool comprises a second refinement coding tool, and wherein the second refinement coding tool obtains a motion vector refinement based on at least one gradient value corresponding to a sample in a reference block of the current block.
 16. The apparatus of claim 13, wherein an affine mode is applied to the current block and initial prediction samples of a sub-block of the current block are generated, wherein the refinement coding tool comprises a third refinement coding tool, wherein the third refinement coding tool is applied to generate final prediction samples for the sub-block by deriving a prediction refinement based on motion vector differences dMvH and/or dMvV, and wherein dMvH and dMvV indicate motion vector differences along a horizontal direction and a vertical direction.
 17. The apparatus of claim 16, wherein the third refinement coding tool is disabled for a first reference picture list of the current block when a dimension of a reference picture in the first reference picture list is different from a dimension of the current picture, or a dimension of a scaling window in a reference picture in the first reference picture list is different from a dimension of a scaling window in the current picture, and wherein the third refinement coding tool is disabled for a second reference picture list of the current block when a dimension of a reference picture in the second reference picture list is different from a dimension of the current picture, or a dimension of a scaling window in a reference picture in the second reference picture list is different from a dimension of a scaling window in the current picture.
 18. The apparatus of claim 13, wherein whether the refinement coding tool is disabled is determined based on values of one or more flags associated with the one or more reference pictures respectively.
 19. A non-transitory computer-readable storage medium storing instructions that cause a processor to: determine, for a conversion between a current block of a current picture of a video and a bitstream of the video, whether to disable a refinement coding tool for refining a motion vector or a prediction sample for the current block by an offset value; and perform the conversion based on the determining, wherein the refinement coding tool is disabled when a dimension of a reference picture of one or more reference pictures of the current block is different from a dimension of the current picture, or a dimension of a scaling window in a reference picture of one or more reference pictures of the current block is different from a dimension of a scaling window in the current picture.
 20. A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises: determining, for a current block of a current picture of a video, whether to disable a refinement coding tool for refining a motion vector or a prediction sample for the current block by an offset value; and generating the bitstream based on the determining, wherein the refinement coding tool is disabled when a dimension of a reference picture of one or more reference pictures of the current block is different from a dimension of the current picture, or a dimension of a scaling window in a reference picture of one or more reference pictures of the current block is different from a dimension of a scaling window in the current picture. 